US gift/estate tax on transferring money back and forth

My parent gifted me a sum of money and then realized they needed it back for a future financial obligation. Based on my (possibly incorrect) understanding of gift/estate taxes, each transfer back and forth is a gift and independent taxable event. I also understand that we both have an enormous lifetime exemption where this ultimately probably does not matter. Nonetheless here are my questions:

1. Does it matter if I return the money in the same year, or a different one? i.e. if I transfer the money back in the same tax year, can we pretend we didn’t make the transfer? Does it matter if the transfers are in different tax years?

2. If I transfer this money back to him, and then I later inherit it, would he effectively be double taxed on this money, as it counts twice towards the lifetime/gift/estate tax?

3. Do I also count this gift against my future estate?

4. If he then transferred the money back to me again, I assume this continues to count against the tax, right? i.e. for tax purposes we should try to minimize these transactions, in the event it ultimately mattered.