Only if no variant appears that has substantial vaccine escape. The thing is that if this is possible there's no level of vaccination that will stop this from h

Only if no variant appears that has substantial vaccine escape. The thing is that if this is possible there's no level of vaccination that will stop this from happening because it's impossible to achieve herd immunity against the Delta variant and stop it from spreading using the current vaccines (they're just not effective enough at preventing people from catching and spreading the disease) - and uncontrolled spread through a widely vaccinated population resulting in strong selective pressure is pretty much the ideal scenario to cause that. Also, if countries aren't testing widely anymore they won't spot this happening because the detection of new variants relies on sequencing of positive test samples.