It's still unknown whether vaccines convey sterilizing immunity. Even if they don't, there will be no political will to institute lockdowns if the people who are getting sick could have been vaccinated. If unvaccinated people getting Covid-19 creates undue strain on the healthcare system, the calls will be for mandatory vaccination, not for lockdowns.

Restricting social interaction and business is a crushing approach to solving the problem, with severe consequences to health and economics. It's brute force, like securing a computer using an air gap. The only reason lockdowns have been used in 2020 is because we have no other options available, but a free and readily-available vaccine changes the calculus.