And suppose we had a three-way people's vote and the result was

May's deal 30%
No deal 22%
Remain 48%

Then what?

The "no deal" option would fall out of the contest, and the second preference of those voters (where they had chosen to indicate that) would be allocated to the vote for the other options. The winner would be the option which now had the largest total. Probably Remain, in this case, since many Hard Deal Brexiters have indicated that May's option is worse than Remain.

I find it hard to conceive that a First Past the Post system would be adopted in a three way referendum. I doubt if the Electoral Commission would even permit that.