As long as the roots were not fully compromised by the drainage problem - doesn't take very long with them submerged in excessively moist soil to smother - then you can expect the tree to leaf out again. All things being equal, I would expect to see budding or new foliage in a couple/few weeks.

Thanks for the reply, Gardengal. I'll keep my eyes peeled and my fingers crossed.

If one drain hole didn't work for you, 10 more won't make a difference. Good drainage and ample aeration are a couple worth inviting to your party, so you probably need to give some consideration to your choice of soil first, and watering habits second. If you can't water your tree to the point of soil saturation and a good amount of water exiting the drain hole when you water without having to worry about root rot and the back-sliding you described, you're sacrificing a lot of potential and your soil is inappropriate. You'll want a soil that's at least 75-85% larger particles - like pine bark, e.g. It will make a significant difference in your plants' health and in your margin for error ..... it just makes life easier.

What I use:
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The soil in the middle is also excellent:
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Al