I wouldn't worry too much about it. Singer may be trying (too) hard to make this movie very much his own but I really can't see him dropping 50% of the current X-Men team. If Charles is going to be in a dark place, as hinted at by McAvoy in his recent interview, I really can't see Alex or Sean being all "We're gettin' real tired of your s***, Mr Xavier" and leaving him. Nor can I see Charles being self-absorbed enough to send them away like he did with Moira. They're his first students and unless this movie jumps more than 10 years in the future (which Singer would be monumentally stupid to do), Havok and Banshee are safe
Similarly, I'd venture that most, if not all, of the Brotherhood members will be back. Definitely Emma. Probably Azazel. And the latter not because he "needs to get Mystique pregnant" (or, as some of our truly classy
board members have so candidly suggested, "get her pregnant by rape"), because I really don't think they need to or should touch upon Nightcrawler's origins in the movies.
First of all, I don't like the idea that Mystique, particularly this
Mystique, needs a man to define her. If she gets rejected by Magneto I don't want to see her just run to another man's arms for comfort. I'd like to think she can be a stronger female character than that, especially at this juncture.
Second, I can't believe that she would just abandon her son. She's not entirely heartless. If she forgot about him, I can't see Charles being so heartless that he would make her forget about him. Emma might be behind it but it seems like so much time dedicated to such a workaround is a waste. The simple solution is to keep on as though Nightcrawler is NOT Mystique's son. It'd upset the die-hard fanboys for sure, but nothing in these movies should ever be done JUST for the sake of appeasing them. General audiences would not notice the change or the absence of this family relationship, just as general audiences didn't notice or care that this Erik doesn't have children.
went on a bit of a tangent there. TL;DR I'm sure both actors will be back to reprise their X-Men roles