It's happened to me three times and I only just started to play with bikes;-)
First two the bush came out in two bit's.
First mech I cleaned I replaced the split bush with a good one from a cheap bent mech I bought.
Second time It happened I super glued it back together and I have pulled the jockey wheels off and cleaned them since, it seems to be OK.
I stripped a M737 mech Thursday. It has been getting muddy everyday for a few weeks now and gear changes were not very good[bit of an understatement]. Any way when I stripped it, the bush rolled off the table, oh well I still had some super glue.
If I get stuck for one I will make a steel bush.