I may be over valuing what they'll get - but I would expect Sergachev to be part of any EK to TB deal... and I would expect Ottawa to want Point as well. Keeping him out MIGHT be doable, if the other pieces are good for Ottawa.
If a 3rd team would come along and offer "young / good roster player + 2019 1st" for Tyler Johnson, and that team is on his list.....
Say the Isles would trade Anthony Beauvillier & a 1st for Tyler Johnson, and he'd take a trade to New York (I think both things are stretches... but I need a hypothetical):
To NYI: Tyler Johnson
To TB: EK
To OTT: Sergachev, Beauvillier, NYI 1st, TB 1st.
That might do it too.
Sergachev, IMO, has to be part of the package. For one: TB needs to clear room on their blueline for EK... and the other 5 all have (at least) limited NT protection. While you'd like Sergachev over (at least) 3 of the other guys - it's not realistic.
Plus, Ottawa will insist on at least one "already in the NHL" young, rising, player. Plugging Sergachev into the hole that EK creates on their blueline just makes too much sense.