With the current high inflation rate, those countries will leave no choice but to accept their fate by adopting and making bitcoins legal tender in their countries if they wanted to save their economies. Most likely it would begin when they see some major success in El Salvador and they will gonna flock to announce their sudden U-turn to cryptocurrency when they feel they have been hit hard by inflation. This is the only way they make their country stable and they will not become like other countries that suffered so much that they are about to lose their national currency and instead use other countries' currency to save their economy.
I am not sure how you conclude that adopting Bitcoin is the only way to save their economies. There are many things they can do except adopt Bitcoin as a legal tender. I am not a particular person about it, but I know how Bitcoin works. Yeah, They can make it legal and invest as well. But, They don't have to invest their country budget or big amount of money to Bitcoin just to save their economies. That's not how it works. They have to understand how it works and be aware of potential risk as well.