If Prigozhin was indeed on the plane, and is now dead, it is highly likely it was no accident, but that Putin ordered him killed. The deal Putin made with Prigozhin's to end the latter's coup made Putin look weak. By eliminating Prigozhin, Putin likely hopes to change that perception.
It's also worth noting that this comes on the heels of the dismissal of Sergey Surovikin and Ivan Popov, two prominent generals believed to have been sympathetic to Prigozhin.
Putin seems to be cleaning house, purging the disloyal (or, in some cases, those who merely may be disloyal). The benefit for Putin is obvious, but there are downsides:
Surovikin and Popov were widely considered two of the more capable Russian commanders. Replacing relatively effective people with less competent loyalists risks further deterioration of Russia's already floundering military effort.
Killing Prigozhin pretty obviously reneges on Putin's deal with him. In retrospect, Prigozhin would have been well advised to reject the deal and continue his "march of justice" on Moscow. The next general or other leader who moves against Putin is likely to pursue it to the bitter end, knowing Putin can't be trusted to live up to any deal. Of course, Prigozhin probably should have known that, too. It's not likely Putin has been scrupulously honest to this point.
Finally, I will note that if Putin did off Prigozhin, the latter merely got what he deserved (albeit not for the reason he deserved it). Prigozhin was a war criminal several times over, for his actions in Ukraine and Africa.