AFAIK Intel and AMD have cross-licensing deals for x86 and AMD64 which become invalid in case of acquisition, on the side that gets acquired.
This means that you cannot acquire rights to manufacture x64 by acquiring either of them.
In any case I find it hard to imagine that regulators in US, EU, UK, China etc. would ever approve this unless Intel was on the actual brink of bankruptcy. e.g. Nvidia wasn't even allowed to buy ARM when the markets they were competing in barely intersected.