Erik Ten Hag would suffer a significant loss if he lost De Gea from his roster for next season; after all, he is not on the Red Devils' retained list. David De Gea's contract with Manchester United expires on June 30, after which he will be a free agent, and his new contract remains pending. United have not yet triggered the extension of his contract, but conversations have taken place, and the club's new contract proposal for David will result in a £375,000 weekly salary cut, which I believe the Spaniard will find it hard to accept. De Gea's contract has been active since 2011, and his presence has been extremely beneficial to the club's growth.
I think Erik Ten Hag already has a potential replacement for David De Gea if he leaves, I think Andre Onana will be the candidate if he will replace De Gea, the current stage is still negotiating because De Gea doesn't want a salary cut with his new contract maybe that's the reason where he will go but we never know if this will be maintained or even let him go in free agency.
I know Erik Ten Hag only wants to overhaul the squad of several players including goalkeepers, defenders, midfield and strikers but we have to know that Erik Ten Hag has a strong instinct which player he needs.