Hopefully, the fees won't skyrocket as people there try to spend their BTC because in that case, they might not be able to use their BTC due to transactions costing more than they got from the government. I really hope this won't go South, but it seems to me that a big conflict and disappointment in Bitcoin is very likely.
Since Jack Mallers' Strike is one of the main drivers of Bitcoin adoption in El Salvador, I guess we could safely guarantee that they will be using Lightning wallets. I've also seen a good number of videos on Twitter with people paying bitcoin to local merchants using lightning wallets.