Opinions on Companions coming back?

On the whole, I think they've all been done very well so far.

I haven't listened to all of the older-Nyssa stories, but what I have heard made for a pretty interesting ongoing story arc and I really liked Nyssa's final departure. Peri's departure in the show was great until the final episode of Season 23 messed it up. But, it also led to one of the greatest Companion Chronicles stories - Peri and the Piscon Paradox - and a truly fantastic Main Range story, The Widow's Assassin. I'm not sure where the arc will end up, but I hope we see some of what we learn in Peri and Piscon Paradox make its way into the arc before Peri departs once more.

Mel's original TV departure just sort of happened out of the blue from what I remember, so I think its nice to have the character come back for a chance at some proper closure. Plus, I really like the dynamic between the TARDIS team - it's a good midway point between the Season 24 and Season 25/26 portrayals of the Doctor so far.

And then there's Flip returning as well. While she's obviously an audio companion only, I really did feel like her original departure was a bit too soon and a little rushed. So, I'm very happy to have her back. I think it's perfectly in-character for her, too. She's younger than a lot of the Doctor's other companions and her brash actions often lead her to make decisions before she's really thought them out, such as leaving the Doctor to go get married. I'm looking forward to seeing whether her new adventures lead her to further brashness or to finally take things a little slower.

Can't speak to the recent Mel stories (yet to be heard)*, but I'm typically against it unless something clever is done with the companions to justify the break like with Charley, Jamie or Nyssa. The far former was given a radically different role aboard the TARDIS with another incarnation while the far latter was shown to have lived her life significantly in the interim post-Enlightenment. If the stories in question could be shunted to before their original departure without issue then there's no reason why they can't be set in their original run like other stories (e.g. Solitare).

It's become something that really bugs me over the past couple of years and I think it was a precedent set by NuWho companions' multiple departures and returns. It started to get to the point where I stop being sad at their departures, started becoming relieved and then became bitterly disappointed when they returned. That's never a good look for your audience. I reckon if a return is going to be organised (beyond a one-off guest appearance), it should be handled with a lot of care and there should be a clear end goal in mind other than "give them a happier ending".

---

* - although if they're placed anywhere other than extremely early on you run into a very interesting bit of subtext. After a certain point, the Seventh Doctor knows that Mel: 

I don't tend to over analyse things too much, but I have enjoyed the return of Mel to the main range with the Seventh Doctor and Ace. So no I don't think it diminishes Mel's TV exit - which wasn't great anyway - and has given us some really strong Seventh Doctor adventures with Mel and Ace together.

If there is a good reason for the companion to come back and a good story comes out of it, then I see no reason not to. And no just as a inferior sequel does nothing to diminish the original film it follows, I don't feel like an inferior story bringing back a companion does anything to diminish their initial exit.

With Mel's recent return, I think they are doing a fair job of fleshing out her backstory - with suggestions of a romantic past and stories that play to her supposed computer skills (mentioned but unused on screen.)
It was interesing to see the balance of power/experience shift between Mel and Ace in the first run of these stories (Life of Crime onwards)... that seems to have levelled out a bit now - although I'm not quite sure where they are set. I was assuming post-Survival - but then one of the recent stories mentioned Gabriel Chase, making me think they were more like S25?

Oh, that's right - You Are the Doctor teased Mel's return didn't it. I forget what point in the 7/Ace's tenure the Hex stories came though?

Personally I'm pleased to see any companion back for more stories if they are written well and the stories are good, without worrying too much about continuity or altered personalities. Within reason: if Adric walked out of the non-jettisoned Zero Room and said 'Earthshock' had all been a block-transfer thingy got up by him at the Master's bidding, I might draw the line.

In the TV era, the two 'never ever return' companions for me would have been Adric and Mel. But thanks to BF, I loved the Fifth Doctor Box Set and enjoyed the first Adric 'trilogy' and the second sounds fairly fantastic from the synopses.

And thanks goodness that Mel returned as she should always have been. I'm not that bothered about how her time with Glitz may or may not have changed her; what matters to me is that Mel the intelligent woman has been allowed to stop screaming and start using her considerable intelligence, exceptional memory and top computer skills as she was never allowed to do on TV, while keeping the sparky humour that was shown off so well recently in 'The High Price of Parking'.

And if continuity is a problem (as would be any serious post-'Earthshock' return of Adric), stories can always be set within the TV timelines rather than after them.