Fiorentina seems to really feel a positive impact after De Gea's arrival as a reliable goalkeeper. Good results this season in Fiorentina with De Gea's outstanding performance made management have to offer a new contract signing. I hope Man United will not regret it. 
Manchester United aren't regretting anything because they are chasing a new and younger goalkeeper from Burnley apparently. There isn't anything official yet but the price isn't that high and they can afford it normally, otherwise Onana is doing the job anyway, he was sometimes good and other times under performing and of course that was the case of De Gea, they rely a lot on Manchester United defence line which isn't effective at all.
Their transfer drama will continue until the transfer window actually opens, new rumors keep popping up almost every day including Manchester's plans to find a new goalkeeper. Onana inconsistent form this season has raised doubts about his future at Old Trafford and there are reports Manchester United are ready to let Onana leave if the right offer comes in and this indicates that Onana position is really unsafe.