I don' think it will be a full rebuild in 3 years based on the ages of many of our key players.
Age is one thing, whether they stay their entire career is another. One of our key cogs doesn’t have a contract beyond this year and Matthews is only signed for 3 years after this (leaving potentially 1 more 1st round to spend as others have alluded). I don’t know how desirable Canada will be to him come renewal or he will be to the Leafs if his injuries persist.