If you think that a merc who is getting paid more than he could ever dream on, would just turn on a boss that can point at someone and kill them, can alter reality, and can detect his very thoughts, oh and will come back from the dead if you do kill him (clone, which lets be honest the merc will have no understanding of how the wizard does it, just that the wizard is basically unkillable). Do you really believe that?Mercenaries are not your friend, not even reliable.
Grab Popcorn and watch the wizard being killed for his fortune.
I could possibly believe the goons would turn if the sorc had gotten the upper hand on the wizard, and had damaged him severly. In that circumstance....maybe (although would the goons really believe the sorc wouldn't just kill them next?). But the wizard + goons are always going to have the upper hand, and there would be absolutely no reason for them to turn on him while the wizard remains powerful.
Movies have created this troupe that mercs are completely fickle and will turn on anyone at the slightest whim. But that is not how it actually works, mercs like to get paid and they like to win....so they will absolutely fight for the guy who has infinite resources and is basically undefeatable..... oh yeah and provides them a protective bubble that makes them completely immune to the enemy's main weapons (globe).