I would say it's at jeopardy more than ever. Consider the reasons for trading down:
-Saves cap space with a lower draft pick
-Obtains additional future draft assets
-Drafting an equally good young player
So this leads to two scenarios
1) Drafting the player from this draft and future drafts to build for the 2020s decade. Basically punting on the rest of the next 3 years, limiting Isaiah's future value as he gets older.
2) Packaging assets for a Unibrow or Butler or George (slightly below their market value)... & going after Hayward or Griffin (at max level money). Considering the cap crunch, this would almost definitely mean it's IT4's last season unless he wants to stay at $8mil/year.
Either way, i see no sign that it's an investment in Isaiah long-term
The only way this could happen is if the package of assets is traded for a very very good player on his rookie-deal. If it turns out that the package is for Porzingis or Towns, then I can see the Celtics having the space to give Isaiah a long-term deal at the price point he wants.