The thing is, I wonder how long he'd be able to hold on to all the Danubian Principalities. He had signed an agreement with Rudolph II recognising him as his suzerain over all his possession's (Transylvania, Oltenia, Wallachia and Moldova if I recall correctly) but the problem was Rudolph didn't trust him.
The Ottomans would want the lower Danubian Principalities back under their fold, and If I'm not mistaken Michael also had troubles with Poland and the Bathory's over Moldavia and Transylvania. Michael was an adept political and military leader but the situation could easily crumble for him as it did in OTL (with his assassination, unfortunately). All his immediate neighbours, even nominal/real allies didn't really trust him. There's no one for him to either. France is for the most part in the Ottoman camp, Russia at this point isn't much of a factor and she'd have to possible face both the Ottoman's and PLC in the prime. Sweden is a bit far off but not completely impossible though.