Thailand will reopen without quarantine. It might be 2021, 2022 or with more problems than expected, even later. My best guess is late 2021 with either zero or 8 night quarantine.
The Junta might well try to keep some useless insurance in place, particularly if they or their friends have financial interests in such businesses. However, eventually the tourists will have a choice of countries to go to. So Thailand either has to be competitive or lose market share.
So far, Thailand has been one of very few countries to allow any kind of entry for tourists.