An answer can be of low quality, but correct.
It makes sense to delete such an answer if there are other answers,
but how to handle the situation where there is no other answer?
I do not think it's a good idea to delete the low quality answer then. Even a bad answer can solve the problem.
I see there is an advantage of deleting such a question:
Because it makes the question unanswered, it would create some motivation for new answers.
But on the other side, the question may now stay unanswered forever.
One way to handle that could be to have a feature to delete an answer as soon as it's no longer the only one. But even then, the low quality answer may be more useful than an invalid new answer.