Hey rfrost,

the way back should be fine, since KRK is almost always deserted. Thus, I never experienced a delayed departurein the last months. Can't say that for LHR so!
So, on one side Munich advertises with the quickest connection times in Germany of arround 25 minutes -> 45 min should do fine but on the other side I wouldn't necessary bet on the punctuality of a flight out of LHR then....

good luck anyhow
cheers
HON_Hunter