I thought the explosion was the bad guys covering the tracks as they made for the helicopter.
Well, yes, but Mike was still engulfed by the blast and there was no sign of him afterward. And I doubt their timing of the detonation was entirely coincidental. After all, Mike was powerful enough to pose a threat to them, so their chances of escape were even better if they not only covered their tracks but killed (or at least incapacitated) their most powerful pursuer.