Well, yes-ish, but it sounds very strange! It is a bit like saying 'what if I am ever ready' in English. It would work in a question such as:
- Fyddi di byth yn barod? - WiIl you ever be ready? ( while looking pointedly at your watch...)
No - the fydda i... indictes that it is a negative phrase.
Usually, though, it would be expressed as ..os na fydda i byth..., which makes the negative aspect even more obvious.