The first evidence I can find of a sale for GTA V was in 2015, over a year after launch, and the first price cut appears to be in mid-2018, five years after launch, meaning that they could continue to sell copies at that $60 for five straight years without much extra motivation for consumers. Whatever you think you the cost basis is for GTA Online, it is still a pittance compared to what they'll bring in.

You don't know if it can.

Funny then that you seem to know that this is some enormous risk instead of probably the safest investment a video game company has ever made.