SLI will either work really terrible without a bridge installed or not work at all. If it doesn't work, the driver will just use one card for PhysX or software can use the second card for parallel work-load processing (not gaming) without needing a bridge.
I'm not telling you how to spend your money, I just hope you didn't go out of your way to buy two 2070 Supers specifically for SLI/NVLink. At this point, SLI is nearly a dead end in terms of game support with fewer and fewer games being released that support multi-GPU rendering. SLI performance scaling is just the same as it was 10 years ago, where some games gain huge benefits, others have very small gains and some games actually perform worse with SLI. Then there is the issue of extra heat generated, which can cause the top card to thermal throttle and lower performance of both, unless you liquid cool the cards.
Question: how would SLI function without a bridge?
I agree with you that investing on an NVlink bridge seems more exotic than ever! However, I am looking forward to benefit from the memory pooling (VRAM) operation between 2 cards. That is an application specific function. Games are an afterthought at the moment. As for temperature increase that could be a real concern...probably underclock a bit and increase fan curves.