We're in a good spot, we're very likely to have a mostly normal late spring / summer.
The danger, however, is that a vaccine-escaping variant gets a foothold once we relax. No one really knows how this could play out, fully.
The evolutionary selection pressures on the virus, pre-vaccine rollout, favoured transmissible variants like B117 over things like the South African variant (with its greater, though not perfect, vaccine escape capability).
Once the population contains a large number of people who are immune to the older COVID variants, the selection pressures will much more favour variants which can partially escape current immunity.
This won't mean we're back at square one - some immunity is likely to carry over, and we don't know how much "genetic room" the virus has to alter the spike protein in a way that retains its core infectiousness but hides it more efficiently from our immune systems.
The real end to this, in my view, comes when vaccine capacity is so huge that we can vary a current vaccine to account for new strains, manufacture it, and deploy it to the population inside of a very short time frame.
We're probably a year or two away from that, but I suspect we'll be mostly ok between now and then with a booster jab some time later this year to cover the SA or other immune-escape variants.
So, I suspect this will indeed be the last total lockdown. Past the summer, I suspect we'll retain social distancing and mask wearing in many settings, for another year or two.