Selling our house-- mortgage question

We're selling our house in Westbury/Carle Place and buying a larger one nearby. For the new home, we're putting 10% down, and for the balance we're planning to have a 30-year fixed mtg for xxx amount, and then a home equity line of credit for the other xxx amount (the amount of the HELOC is the amount of money we plan to have leftover from the sale of our current house... the HELOC is to cover us in case our house is not sold by the time we close on the new one)

So here is my question-- I know that closing costs are proportional to the size of the total mortgage you're carrying at closing. What if we manage to sell our current home in time to HAVE the money available at closing that we would have otherwise been using the HELOC for? Do we still have to close on the HELOC, or will our closing costs only reflect the 30-year fixed that we will *definitely* be having?

Thanks in advance