then the sentence is banishment and degradation into indolent, idle fool.
"sentence" is the punidhment given to someone, usually by the courts.
If his wife does not like London, then he will be there alone.
then the sentence is banishment - bansishment is being sent away, separated.
He will also be degraded - down-graded, become less, in that he will be idol, not seeking activity (indolent)
If his wife does not like London, (and so does not stay there?)
he will be alone, taken from her and become no more than an idle person
and degradation into indolent, idle fool.