You can be quite sure that if the plant desperately needs to have its visible parts pruned, the parts you can't see, the roots, are in a state of need even more dire.

If I had to outline a plan for you, this is what I would suggest:
A) If the plant is severely root bound & suffering because of it, I would pot up now as a temporary measure to help a little with vitality.
B) Move the plant outdoors as soon as temperatures allow. That is, as soon as night temps are reliably above 55* - sooner if you have the wherewithal to move the plant in and out to avoid temps below 55". This will help the plant gain strength.
C) Repot/root prune around Father's day.
D) Prune the top in mid-July.

It's also possible your plant would benefit from a thorough flushing of the soil; this, especially if you've been watering in sips and not flushing the soil at every watering.

This is just a very general recommendation. I'll provide more details if you'd like, after you decide if you wish to move forward with a major rejuvenation effort that is planned around the plant's energy/growth cycle. While Scheffleras are pretty bullet proof, there is little sense in moving forward and tempting fate or extending the length of recovery because of less than ideal timing.

I think you'll find the thread I'm linking you to below of value.

Al

Here is a link that might be useful: More to consider here