As far what might constitute a fair deal, we've seen goalie trades in the past yield some pretty underwhelming returns, so there's no real guarantee that the return for Hellebuyck with one year remaining would be a runaway win for the Jets. If the Leafs are offering a 40-goal winger up in the deal, they might not need to add anything to put together a competitive offer. However, with Murray, Samsonov and Woll all under contract for next season, it might make sense to work out a bigger deal surrounding Samsonov and Nylander for Hellebuyck and Dubois.
This deal gives the Leafs a legit 2C and allows them to shift Tavares over to the wing and a true #1 netminder who can shoulder a heavy load this season and provide a veteran presence for Joseph Woll to study under. The Leafs can then move Murray in a subsequent deal and roll with a Hellebuyck and Woll tandem.
For the Jets, they'd be bringing in a good young winger to maybe entice Scheifele to extend and a quality young goaltender in Samsonov to soften the blow of losing Hellebuyck, who isn't re-signing in Winnipeg anyway. The move doesn't exactly set the Leafs up for the long-term, but it does give them a chance to compete for a Cup next season with what could be an ultra-competitive lineup.