The goal at this point should be to flatten the curve as much as possible to prevent overwhelming healthcare until a vaccine is developed and tested. Nobody thinks this is going to be a permanent measure.
Consider raw r0 of 3.0. Each case infects three other people. But as more and more of the population gets infected and acquires immunity the infection rate drops. Say half the population is immune due to prior infection. The rate is now half r0 = 3.0 * 0.5 Left unchecked 66% of the population will get infected and then the disease dies out.
Social distancing, hand washing, quarantine reduces r0. And reduces the total number that the virus can infect before is dies out. Cut r0 from 3.0 to 1.5 and the number of infected goes from 66% to 33%.
In the US that would be 100 million people. And maybe a million fewer deaths.
Scuttlebutt is China and Taiwan due to high early compliance have r0 down to about 0.3, which means the epidemic is in a state of exponential crash.
If a vaccine wasn't even in the picture flattening the curve would help with these things.