If your program is allocating so much that you can exhaust a 64bit counter, you have a seriously bad program plus a serious memory leak. Exhausting the counter would be the least of your worries.

Practically speaking you could never allocate memory that fast, a memory allocation is going to be well over 1000ns on average.

Then there's the little matter of address space. Pointers on x64 are limited to 47 bits, meaning that if even you had a magical memory allocator with no book-keeping overhead, and all your allocations were 1 byte, you'd run out of pointers first. The actual virtual memory space is limited further on many operating systems, but you're still always going to be well short of 64bits.