The best-case scenario for the Lightning here is to obviously not trade Stamkos but if they were to trade him, their best return would have been Ryan Callahan and Dan Girardi. Ironically enough, both would be playing for the Lightning in 2018. However, they were past their prime at that time. If they were with the Lightning during their prime they could have certainly helped them out immensely but only for about 5 or 6 years after the trade.
It is difficult to determine what exactly is the worst-case scenario. First off, Evgeny Grachev only played 34 career games scoring one goal so he would certainly be a part of this deal. The other piece would have had to be Michael Del Zotto or Brandon Dubinsky. Del Zotto likely would have been slightly worse to acquire despite having a higher peak in the following years.