RNH is a legit top six forward. The Oilers need to add another regardless, as well as a starting goaltender, likely a top four defenseman, a solid third line center, and a couple of solid bottom six players.
Letting RNH walk means you now certainly have to add two legit top six forwards, and they're both likely to be more expensive than RNH with at least 4-5 years term. This assumes Edmonton is able to land the big fish free agent targets they want while now bidding against 31 other teams in the process which for a long time now appears to be tough sledding. Then you need said players to mesh well with the locker room, something we already know RNH does very well. You know he's a good penalty killer, you know he gels well on the PP, and you know he can fill in as a center if heaven forbid anything happens to McDrai. With another actual top end winger on the team this also helps him run a second line better than trying to have him center players who should be in the bottom six, if the need arises. We hope Yamamoto can be a top six guy but you need to bump him down until he shows you otherwise.
I think most of us Oiler fans know what the laundry list of needs is, and I think most of us acknowledge it's unreasonable to expect everything to be filled in one go this summer. That's a lot of potential turnover in one offseason. Letting RNH walk only makes it that much harder, and adds another substantial need on top of the already large list.
Most of us think its a contract that will be moveable years down the road if need be, and if not you can consider a buyout, but that's likely at least 4 years away and the McDrai window is 4-5 years currently. So any concerns about the backhalf really don't matter if the team hasn't won anything or become a legit threat by then as there will be far bigger problems in Oil Country.
RNH is a solid complimentary player. People can say what they want about playoff production but the fact is playoff success comes from full team success, and having RNH taking up 1 of 12 forward spots doesn't change that. You still have to make the playoffs, and he absolutely helps with that.