Id say to get the games and thesee if your upgrade is nessisary. Even if your gpu has trouble maintaining 144hz with max settings, reducing settings will help.
Absolutely agreed with this. Don't buy what's available now hoping it'll serve you in the future, or with some idea of future-proofing.
After all, by the time you get games that are too much for your Vega 56 to handle, who knows how much prices will have come down on current generation cards, or if another generation of cards are out by then.
Wait until you get the games, and then see if the Vega 56 can handle them. If so, great, you've saved yourself a bunch of money. If not, then the same money you would've spent today will buy more graphical horsepower per dollar in the future.