1. Are masks suggested to protect the wearer from contracting the virus or to prevent the wearer from spreading the virus?
2. Are vaccinated individuals still able to host and transmit the virus, despite not contracting the disease caused by the virus?
If that is the case, herd immunity cannot be achieved with vaccinations.
Vaccinated people have a lower viral load, thus are less contagious, thus lower the R1.
If the r1 is below 1, then you eventually get to herd immunity. The more vaccinated people there are, the less dangerous the disease is, and the less contagious it becomes.
Herd immunity is not binary: it's a gradient, and if you are on the right side, things get better.
Lets say being vaccinated halves your chances of passing on the virus compared to an unvaccinated person. If almost all the population get vaccinated, we can ease the lockdown to the point where we tolerate doubling the chances of re-infection. The lockdown easing and vaccination effect should cancel out. If vaccination reduces your chances of passing on the virus by 10x, then we can tolerate a 10x increased risk due to easing lockdown measures.
Worst case we may have to retain some limitations in social contact for a bit longer, but hopefully nowhere near as onerous or we've had to so far.
Whether your immune system knows how to fight the virus from previous infection, or from a vaccine, it can take time for your immune system to kick in and fight of a new infection. During that time you might be infectious.