I have a swapped jdm zc in a 91 crx si and my passenger side engine mount bolt broke off into the tranny leaving no room to even get a tread for another bolt, so this led to my front tranny mount bolt to pop out, I put that back in and it still hits hard when shifting with ease. my rear, front and drivers side mounts are tight an fit (btw) but how long should they hold for.

 

I would not chance it. You may end up causing more damage and you will have wished you just fixed the problem in the begining. You can easily drill the broken bolt out!