Well, I suppose it’s all relative:
What happens to a bishop who resigns? Does he go back to doing pastoral work? Or does it mean he’s no longer part of the holy orders?
Was it an archbishop who said “My vow of poverty has brought me wealth beyond measure, my vow of obedience has brought me power beyond that of princes, and never mind what my vow of chastity has brought me?”
What does that even mean? 
Bill Door, as far as anyone has shown in this thread, there’s no reason to believe that anyone has ever said, “My vow of poverty has brought me wealth beyond measure, my vow of obedience has brought me power beyond that of princes, and never mind what my vow of chastity has brought me?”
Nothing erases Holy Orders. Their reception leaves an indelible mark on the soul, in Catholic teaching.
A bishop whose resignation is accepted by the Pope is still a bishop, but he is not the Ordinary of a diocese. His former see, his former diocese, is vacant at the moment the resignation is accepted.
What he does afterward is up to the Pope, who can assign him elsewhere, to a staff position at the Vatican, or to a position as an auxiliary bishop subordinate to an Ordinary of another diocese, or even to residence in a particular parish with no assigned duties.
He could still say Mass, hear confessions, and even validly ordain priests. If he was not given the assignment to do so, then those acts would still be valid, but not licit.
He goes and does what his superiors - likely to be his new bishop - tell him to do.
When Eamon Casey, at the age of 66, resigned as Bishop of Galway after revelations that he had fathered a child, he went to South America and did missionary work. Then he worked as an assistant priest in a parish in England. Now he lives in a nursing home. He has dementia.
Brendan Comiskey resigned as Bishop of Ferns in 2002 over his failure to address clerical sex abuse cases in his diocese. He hasn’t worked in ministry since. (He was 67 at the time of his resignation, and an alcoholic.) He lives in an apartment which he owns himself. He would, I imagine, have a pension from the diocese.
In general, I suspect it depends on (a) the age and health of the bishop, and (b) the reasons for the resignation. In general, a retired bishop will have the same right as a retired priest to a pension and the provision of accommodation, but if his age and health (and the reasons for his resignation) permit he’ll be expected to engage in some kind of pastoral work.