Take it outdoors. Look for a spot in open or dappled shade, bury the pot so the soil lines inside and outside the pot are roughly even or the soil in the pot a little lower than the surrounding soil. When it starts to push new growth, start fertilizing. If it's going to turn around, that should do it.

Al

Basal sprouts often occur when the top is dead, but not always. They're good 'insurance' that you'll have a viable plant, even if the top dies back to the base. If you get new growth popping from the existing trunk, you can rub the basal sprouts off with a thumb or prune them with a pair of scissors.

I'd wait and give the tree some time to reorganize before you fertilize, but A) do start fertilizing as soon as you see growth being pushed from the trunk, or B) fertilize if after 3 weeks the trunk isn't back-budding but the basal sprouts are growing.

I suspect your issues are related to poor root health as a result of lengthy periods of soil saturation. The reason I suggested that you put the plant in the ground is related to the fact that from the perspective hydrology, partially burying the pot turns it into a raised bed; this, because the earth will act as a giant wick and remove any perched water that would otherwise remain in the pot under conventional container culture. Soils that would be virtually unusable in containers because of excess water retention will often do a stellar job in raised beds. Most container media aren't that smart, so they're easy to fool if you know the tricks.

Al