David de Gea is the longest serving player at Man United and I'm not sure if MU will really let David de Gea leave MU. I heard that David de Gea wants to continue his career in the premier league and I also haven't seen any rumors that Man United really will release this goalkeeper to another team.
so this news is not certain and for me it will not happen because even though he is old, David de Gea has a lot of experience at the red devil and it is difficult to leave.
I think Man United will definitely still hope that De Gea will continue his career with them but what really becomes an obstacle is De Gea's huge salary which Man United might be reluctant to accept. So the final decision rests with De Gea himself.
If he still wants to stay then he has to accept the contract offered by Man United (which of course there will be a wage cut). But if he still cares about his income, it means he has to leave Man United.