If Lukaku perform good i wouldn't buy Dybala at first place. But now since you did, it all depends on your 2nd striker, can he replace Dybala if he get hurt?
Though Lukaku scores quite alot of goals, but it seems Rashford is doing a better job as a 2nd fast striker. Lukaku tends to miss alot due to his bad first touch
Buying Dybala is a clear indication you don't think Lukaku is good enough so where is the problem. Mind you personally I would try to squeeze a little more out of the market.
Was looking to swap Lukaku for Icardi but knowing how much he will cost and how much ill most likely get screwed in the market for lukaku i am now having 2nd doubts.