The supermajority getting it, and the survivors then having resistance to greatly slow any future spread is what's known as "herd immunity". Which will eventually & naturally make things less spikey, and fewer infections/deaths. There's plenty of diseases that have gone this way through history.
The way a vaccine alters this: (running with the fairyland example of a perfectly effective vaccine that everybody can take tomorrow) is that makes group #4: people whom don't ever get the disease and can't or spread it, keeping themselves and the population at large much safer. In this fairyland where everyone could/would take this 100% effective medicine tomorrow, it could accelerate opening and get everything back to the old normal.
Obviously fairyland doesn't really exist. Any vaccine is a looooonnnnng way out for development, testing, approval, mass manufacturing, distributing, get people on board, etc. And it will also likely be messy with flawed protection and possible side effects. So even getting a vaccine to people will be a phased approach.
All in all: we're stuck with the new normal for 2020 and 2021.