With 10 times bigger blocks, fees still won't be zero. There will be more transactions and more people could use Bitcoin. That means more people pay fees, so the total fee will still pay millions to miners.
What's plan B in the plausible scenario that the people that use it as currency don't do a 10x?
Plan B will be a slower increase in hashrate after the next halving, that's all. That's not such a bad thing: it will still be improssible to do a 51% attack, and the energy consumption may drop a bit. Bitcoin will just keep working.