No I think Juventus should sign a new goalkeeper because Buffon is too old now and has no long future in the club. After buffon retire, Neto will be the one and only goalkeeper in a senior team, and with sign Donaruma will be a really good choice. Beside of to weaken AC Milan, Donnaruma is deserve to play for juventus so he can fight with Neto for the position.
Buffon will probably play like forever and I think that it will be atleast 5-6 years more until his body decided to retire. There is no sign that he will retire now and he is still great with his position so there is no reason for him to retire. I doubt that even juventus will let their legend leave and retire soon enough