Spending his entire career in Edmonton and having little to show for it in terms of playoff appearances/success. He could want to leave for any number of reasons.
If the Oilers still aren't good in 2 years when Nuge becomes a free agent then we'll have much bigger worries than him leaving.
Bottom line is that you can't worry about stuff like that now. You don't make this pick based on Nuge possibly leaving in 2 years or what any current needs are. You draft the player who you think will be the best player long term.
To me, the best all around players in this draft outside of the top 3 with Byram included are Turcotte and Krebs. I'd be perfectly happy with Dach, Cozens, Boldy, Zegras, Caufield or maybe Newhook (I need more viewings of him) but Turcotte and Krebs seem like the type of players who you can trust in all situations but also drive play at even strength. What I also like about them is that they aren't afraid to drive the net which is something really lacking on this perimeter oriented team.