The best part of this whole thing is looking at their current cap structure. When it comes time to re-signing him, there is no way they can add 10mil onto their roster without significant changes to their major players. There are already so many roster players on 0.6 - 1.8 mil contracts. And the contracts that expire by the time his ELC is up are not all that terrible of contracts; they will need to be replaced, and cannot be replaced with equal talent and major savings.
https://www.capfriendly.com/teams/oilers
I won't even talk about replacing players coming off the books on contracts under 1 mil, because they will be replaced by essentially the same price tag. That leaves:
Matt Hendricks 1.85
Mark Letestu 1.8
Patrick Maroon 1.5
Zach Kassian 1.5
Mark Fayne 3.625
Kris Russell 3.1
Brandon Davidson 1.425
That's a total of 14.8 mil coming off the books. If they went to the hockey thrift-shop and only replaced these players with 1 mil players, that's 7.8 mil in gained cap space.
Again, these are not exceptional players, but a good secondary is key (especially when your cap structure is heavily front-loaded!) and I can't imagine this team being able to lose these players for barely-NHLers. In particular, losing those 3 defencemen would be a huge step backwards for that team.
So at this point, by replacing those expiring contracts with farm kids, they have gained 7.8 million in cap space. They already have about 3.38 million in cap space. If you add on the yearly cap limit growth, that will add up to the total amount needed to re-sign him.
Things not yet considered: re-signing players who might be in line for a raise. Those would include players like: Draisaitl, Nurse, Benning, Simpson, Musil, Slepyshev, Caggiula, Pitlick, Parakinen, Gryba, Gustavsson. A few of those (Drai, Nurse) will certainly chip away at their cap space, and might force them into unwanted bridge contracts.
In summary, they either need to lose valuable top-end players, or lose too many secondary-role players. The end result is the replacement of several current established NHLers for kids on entry-deal contracts, the question is how big of a step down those replacements will be.
This means that that the Edmonton Oilers of 2018-19 are going to have a real tough time being better than the current group. Their window is the current season and next season. The only way they extend that window is by developing players to contribute to their team on cheap contracts.
And it all comes down to that. The Oilers needing to develop players.