I don’t know what to expect of Covid. It could nearly completely disappear or linger for years...but yes, one of the possibilities is that it lingers, maybe in a different mutated form, and possibly even one in which a yearly vaccine, like the flu, is given...or it could turn into another cold virus. Like prior coronaviruses.
As far as drugs like Tamiflu, they’re most effective when given earlier in the flu/viral infections, within the first 2 days. They’re not completely ineffective as a treatment when given later, as a treatment after infection has fully taken hold after 2 days, but that is significantly less than ideal.
This is just basic stuff from the package insert and the CDC, of which I’m sure you’re already aware