HELOC on principal residence - great, but what happens if I move?

[Felipe A.]

I am exploring opening a HELOC on my principal residence allowing me to make a nice down payment on properties down the road.

However, if I move, I have to pay off the HELOC before satisfying the mortgage on the old house. If I used $50k on a HELOC on down payments on rental properties, I need to pay off that $50k off. What is the common approach to paying this off? I don't believe I can refi the rental properties notes to account for this $50k b/c I will exceed LTV ratios. Thoughts?