In my opinion, a squadmate returning after being gone for a game isn't a bad thing of itself, and it actually could be awesome if handled well (like Wrex returning during Citadel)
But there has to be a good reason for them to go, and an even better one to explain their return (that last one failed with Liara)
Sure, I'd love to interact with squadmates that left, maybe have em as temporary mates if they are a specialist you call for your mission (Legion, Mordin, even Grunt)
Or have them do their own thing entirely, if thats a logical continuation of their story (Wrex and Jack)
But they don't necessarily have to be in a mission, they could also just be a Conrad or Dr Michel, who we can simply converse with, or even something as simple as having them on the comm if we want their advice/opinion (like Hackett or Anderson)
Basically anything is ok with me, as long as it makes sense with the people involved and the situations they've been in.