For RCs (and for Anglicans, but let’s pass over that for a moment), valid ordination imparts an indelible character; he is a priest (if validly ordained), forever. This (and I am open to correction) holds even of he becomes a schismatic, apostate or heretic, as I read Ott. I am not aware that even the act of degradation would affect this, degradation not removing the character, but the right to exercise it…
The sacramental power to confect the Eucharist remains, providing he holds to the minimum of intent, *facere quod facit Ecclesia *, and assuming valid matter and form. Intent is usually assumed to be valid, by the act, absent some point that permits a determino ex adiunctius. Generally the Anglican form for confecting the Eucharist is considered weak by the RCC, but I am not aware it would be considered invalid; indeed I have read the opposite, in Michael Davies. The matter would not be an issue; unleavened bread and fermented wine. Generally, what I’m saying is that the Anglican Eucharist is not judged invalid on the points of matter, form, or intent, but on the minister; who is not judged to possess valid orders. A RC priest, now in the Anglican Church, would possess such. Hence (as I understand it) the Eucharist he confected (other points being equal) would be valid, but illicit. I am open to correction.
GKC