I understand that proposals are deleted after a period of inactivity. My impression is that this allows someone else to come along with a new take on a similar idea that may work. But what about a situation where a proposal is deleted and the same user immediately creates an identical proposal? That doesn't strike me as very productive, but I haven't been able to find any statement on how that is handled.
If you think you can create a similar proposal with the same general audience, that will do better, there is nothing stopping you from doing so. It is not unusual for several similar proposals to be moving forward on area51 at the same time.
If the proposal has timed out at a 12 month window etiquette generally allows the original proposer to propose the relaunch. I have personally occasionally proposed a relaunch near a 12 month timeout that was slightly different then the original. Proposal activity and discussion give clues as to what the most appropriate action might be.
In any case, anyone can propose anything. If you have a better idea, go for it.