I don't think Robespierre could stay in power more than he did OTL... He was turning the French Republic into a Dictatorship while not admitting it. Besides, as was said before me, by the time of his fall, Robespierre had lost the support of everyone except his hard liner jacobins, which were very few.
Besides, I'm not really a fan of the idea of having him staying in power... The man and his collegues provoked a slaughter : the law of suspects had the death penalty applied for every crime, even if it was only based on a denounciation (at least from what I understood).
Let's also not forget that most common image we have of Robespierre is a satiric picture of him beheading an executionner with a guillotine next to a monument saying "Here lies all of France"...