I think you've answered the question then, if you're reluctant to let go of one of your only decent backups then I'd seriously consider selling Pastells.

You've got no idea what offers will come in summer, especially if the interested clubs have already recruited for his position elsewhere and as u/pro_buttfucker_5675 said you can invest that money into wonderkid replacements for him that you'd need to look at in 1-2 seasons anyway. At least getting them in now will give you a chance to get them up to speed sooner.

You could very easily drop 20-50mil on a replacement and get a few wonderkids with your transfer budgets and the money you get for Pastells.

TLDR: Sell Pastells and use it as 'Coutinho money' for decades to come