Would you continue IO monotherapy in a patient with metastatic RCC started on first line IO-TKI combination but with poor tolerance to TKI?   

Yes, definitely assuming no limiting irAEs. There is clear activity to IO monotherapy in mRCC as evidenced by KEYNOTE 427 and other datasets. Combination therapy is superior, however, so dose interruption/modification of the TKI should be attempted before discontinuing permanently.