A rebuild should only happen if somebody upstairs screws up. Maybe Poile retires and his replacement messes the bed. (At least now it won't be Fenton! Bullet=dodged.) But I don't think you plan for a rebuild, ever... not in 3 years, not in 5, not in 10. An NHL GM has enough tools at his disposal that it's incumbent on him to keep on winning, making changes on the fly, cultivating a prospect pool, managing his payroll, just keep on truckin'.
Most teams do eventually hit the skids, however. Because they screw up their drafts or their development, or they have enough players who drop off too soon, or sign too many bad contracts. If we win a Cup and all those fat long-term contracted guys we have get complacent, it could happen to us too. Or any of a host of other things could go wrong and we land in a rebuild. But again, it's because things GO WRONG, not because it's part of any long-term plan.
The only major risk factor on my horizon right now is goaltending... Pekka can't go on forever and while Saros is as good a padawan to have on hand as it gets, until he fully shows he's ready to cut off his braid, it'll be our main question mark in the medium term. All the other stuff we nitpick over isn't really important. We can ride out a Turris contract or let Smith/Granlund walk, and losing our 9th-best player to Seattle isn't going to drastically change the team's fortunes. But not having a solid #1 goalie could become an issue. It's a lot harder to just go sign one as a UFA (Bobrovsky!) or wait 7 years for one to develop from within.