No GM can or should plan to not compete for 3-4 years. In 4 years, all of KK, Suzuki, Poehling and Brook will be off their ELCs, Domi, Gallagher, Danault and Lehkonen will have received new contracts and cap hell will be approaching. The time to start competing is now. Build now. Improve now.
If moved, Petry with three years at $2.75M should yield WAY more than a quality prospect and a late first. WAYYY more. Even at $5.5M he should fetch somewhat more.
As for the expansion draft bogeyman, don't worry about it. We will lose exactly one player, just like every other contender. If our lost player if a highly paid vet, then we'll gain the cap space to replace him.
The point is that Petry, when we are ready to compete in three or four years will no longer be the Petry you have now, or we won't be that Petry for very long still. Get a young LHD to be that Petry, only on the other side (where you have a distinct weakness in the system,). for then and for the full length of the window that will be opening up at that point.
You can disagree about the return, and that's fine, but a bluechip prospect to make the NHL at LD and a first rounder would certainly help the team going forward as early as next year. That prospect could benefit from Weber mentoring him while he can. For example, TOR's prospect, Sandin (just an example of a blue chip prospect at LD) could play alongside Weber next year. he might not be lights out yet, but that's what development is as the team matures towards being a legitimate contender. I also don't see where that would be worse than the committee playing with Weber this season?
I really don't see where I am advocating not trying to compete for 3 or 4 years. Shifting strength from the right side to the left side on D, when you have perceived depth on the right side is an attempt at strengthening the team, not weakening it.
The other option is to trade for a veteran LD, like a Brodie who is somewhat younger than Petry and will be around for longer (up to 7 years at a productive level). He'd be worth protecting at the expansion draft as well. Petry for Brodie as the important pieces in a trade with CAL, for example, might be worthwhile since Brodie is currently being used on the right side even though he is a left shot. CAL needs a RD.
Under this scenario, Brodie would be a replacement for Petry, only on the left side to balance out the team's strength on D. It would strengthen the team immediately, IMO.
In the immediate future, Brodie, then Mete, then Kulak on the depth chart for the left side would be considerably stronger than Mete, Reilly, Kulak. On the right side, it would be weaker with Weber, Juulsen, Benn, for the short term, but the near future would see Weber, Juulsen, Brook and would gravitate towards Weber, Brook, Juulsen, all with the hope that Brook could eventually be groomed to replace Weber, leaving Brook, Juulsen, Fleury down the line.
IMO, Romanov will be an NHLer, but his ceiling is still undetermined. It would end up being Brodie, Mete, Romanov or Brodie, Romanov, Mete on the left side. Significantly better than what we are currently seeing.
All of this, barring some prospect's meteoric rise through the system. I think Harris is too much of a project, for example, to slot into a future line-up.