Effectiveness will most certainly go down, and at some point there will be a variant against which the vaccines offer virtually 0% protection. I will even go further, ON RECORD BTW, that there is a big chance that we will get variants against which natural infection DOES provide immunity but the vaccine doesn't, and there's even a smaller chance of one the other way around. The actual immune response between vaccine and natural infection is measurably different, in a few ways that are fascinating.
As far as masks go: of course any time you put something in the path of something else, it's going to affect it. In the case of Covid aerosols, the difference can be anywhere from 0% (mask on the chin) to some number based on how you define "work". If you're talking a quick visit to a well ventilated big store, you could get close to 99% prevention of a sick person infecting someone else. When you're talking cloth masks, homemade stuff, at a small Starbucks, you're gonna be way lower. When I saw some of my colleagues (musicians) in a small studio for 6 hours together with mask on, I would say you're in the single digits.
Just to show you guys I'm not crazy, I've had arguments with a friend in Holland FOR masks, because there the infection rate had been SO low, that trying to buy time to get everybody who wants vaccinated, WAS worth it. And in the end, so far that has panned out. In my opinion, the best way to estimate infection rates in a country, assuming it delivers trustworthy numbers, is to look at deaths per million. Los Angeles has 2.6x the deaths that Holland does.
The bottom line is, masks can work on flattening a curve, if everybody would wear N95, properly put on and off, it could be quite effective. What we did in LA was NOT effective; we wore masks for 17 months and more than 2/3 got infected anyway. This is what people mean when they say "masks don't work".
And one more time, a flattened curve representing exponential growth will STILL get to 100% just a little later. If we needed time to vaccinate more people, you might have a point, but in my opinion it's time to get over it.