Is it correct to say, "so much time has gone by", or should "by" be replaced with "bye?"
What are some other things someone can say with "by" at the end?
"So much time has gone by" is correct. This would be understood to mean "so much time has elapsed" or "so much time has passed".
"So much time has gone bye" would be (at best) a sort of pun, based on the personification of the elapsed time. (picture time as a person, waving good-bye as it goes past. You would say that time has gone 'bye!'). You would have to write this using quotes around the word "bye" to make it clear that it was meant to be a play on words, and not a typo.
Some other phrases which can end in "by":
I presume you are talking about the preposition at the end on the sentence?
In response I quote Winston Churchill:
This is the sort of pedantry, up with which I will not put.
But seriously, the idea that prepositions cannot occur at the end of a sentence comes straight from an era when grammarians tried to force English into Latin grammar (where you really cannot put a preposition at the end of a sentence).
The "rule" is completely archaic.
Are all perfectly acceptable, and whilst, "I live by this rule," is more regular it is no more correct. Certainly "This is the rule by which I live," is more inelegant and has worse flow than the version with the "unlawful" sentence-ending preposition.