Lazar is easily exposed, and without worry, either. Vegas won't take him.
We're most likely losing a defenceman. I can't imagine there are too many 3rd-line/4th-line forwards on our team that Vegas would want more than Methot (or Ceci).
I think the best course of action would be going 4-4. A lot of people ignored the possibility early on because there was an assumption that Ryan had to be protected, which would have led to us losing one of the big four forwards in Turris, Brassard, Stone, or Hoffman.
Going 4-4 keeps our top 4 defense together and keeps our core forward group together. Whether we go 7-3 or 4-4, we are destined to lose a valuable player, but losing a forward is a much easier problem to correct than losing a top 4 defender like Methot.
We couldn't even solve our need to find a bottom pairing guy this summer via free agency so I think it is safe to say we're not getting a Methot replacement via free agency in what might be the most competitive July 1st in recent memory.
I would much rather lose one of Dzingel, Ryan, Lazar, or Pageau than lose Methot. We could also lose Smith to Vegas, but he'll be a UFA so that is a bit more of a complicated issue.
If the plan is to trade for help after losing Methot, the trade would cost more than any one of those forwards above.
The only reason to leave Methot exposed is that the team feels Chabot or Englund are ready to be solid top 4 NHL defenders, which given historically how well defenders at their age perform sounds like a bit of a stretch.