Maybe the situation would be that the blanket would just tear off of
them

I think so.

and all would be fine

ell,except for the banket of course<smile>

Should I just stall them during an entire raining instance, then
let them out when it's dry enough?

I think that depends on you and what would make your horses happier.
Rainsheets are great against wind/rain...horses' 2 biggest
environmental enemies.....oops,in my experience.

So some blanket their horses WHILE in stall if too cold or windy out
(& possibly wet)

Yes,but again it depends on the situation.Remember in the stall they
don't move around much to keep warm,the way they can outside.So they
*may* need a stable rug for that reason.Maybe not,though,if they have
good coats.

Lorna