Maybe, but I'm not assuming he'll sign just because United make an offer, I just think were potentially more attractive than you have us.
We're now a PL club with a clear pathway to the first team and if we do happen to be relegated that pathway becomes even clearer to a Championship side with 3 years of Parachute payments. Alternatively, if he has a huge breakthrough season in the PL, there will be significant interest.
He's 19 (20 to keep Bongle happy

) and dropping into an established PL squad while developing is a risky move for him from a development perspective.
With us he will be playing regularly, be that on loan or in our first team squad, but he'll likely earn less but at 19 is that his main driver? I'm not so sure.
A longer contract with us doesn't actually tie him into anything, aside from better pay, higher standing, and us invested in his further development this season. If a big move materialises it's not like we could or would refuse anyway.
For him and us, it does feel like a rare no-brainer on both sides.