I think he deserves a couple of more games before switching back to Onana unless he can't perform. Give everyone a chance to judge him properly and hopefully has positive impact on Onana.
We did that with Henderson for a brief period with De Gea and that works wonder. De Gea responded well and came back with couple of player of year achievements.
If Onana don't respond positively, then it is also a sign that he can't make it at this level.