The Thai ไป,-'Pị' as used in 'di pi' and the English 'good bye' sound the same and mean the same. Is there a known etymological link?
Bpai comes from Proto-Tai pai "to go". This is clear from its various cognates in other related languages.
Bye comes from a shortening of "God be with you" > "God be wi' you" > "God b'i'y'" > "God by", which then became "good bye" by analogy with "good morning", "good night", and so on. We have attestations of the different stages of the process, so it seems clear that this etymology is correct.