Herd immunity exists when enough people are incapable of re-transmitting a disease that the R number is below 1, even when we're back to a normal way of living.

It may be that the vaccines will be incapable of giving us herd immunity, but they may allow us to keep the R number below 1 with much less extreme social distancing and lockdown procedures.

Without the vaccines, the only way to get rid of this pandemic is through severe economy-damaging lockdowns and liberty-encroaching contact tracing and quarantining. If we can achieve the same thing with vaccines plus just having to wear a mask when near other people, then I would say that vaccination would still be a moral obligation, even though we haven't achieved herd immunity.