Probably (brick) stones will fall out if you just remove the beams.
Likely, not the entire wall will collapse, but a few rows up, mostly in the middle, until a rough "arch" has formed.
Among other things, it depends on how wide the windows are, but if the brick beams have started to sag, it is a bad sign.
So, I would have supported (the structure) beforehand, just to be safe and because it's probably less work than fixing it afterward.
How do you support it then? Actually, not so hard..
Start by removing every third brick above the brick beam. You can do this with a chisel and hammer.
Then insert 45x75 beams, which "stand up" through the holes. Support them from below with, for example, 75x75 beams.
Now you remove the brick beam and put in the new one.
Pull out your wooden beams and brick back the bricks.
Done.
/ Fredrik