Is there any difference between "has gone" and "went" in this context?
When using the present perfect "has/have gone", the implication is that he has not returned and is still in Europe. With simple past tense, there is no such indication: he may still be in Europe or he might have returned.
Incidentally, you would normally use "Mirek went to Europe on business." when the time of the action is understood between both speakers, so the context might indicate whether he is in Europe or back where he came from.