1) After paying the Khoms of the 50k, the remaining is 40k, not 50k. However, as you said, you do not need to pay the khoms of the 60k.
2) If you paid the khoms of 50k (10k), then the net amount you have is 40k, not 50k. Regardless your intention, If you spent this amount the next year, you can replenish it from the earnings of that year. If you again spent the amount in something other than buying the home, then, it is gone.
3) Recycling is exempted once only. Hence, if you spent the recycled amount, then you can not replenish it again.