On the last part of the question, God would not send that person into a situation, if He knew the holy person would thereby end up in Hell. The hypothetical was based on a short stay in Purgatory, not a loss of salvation.
It is not unfair because the holy person desires to do the will of God, even if it means more suffering for him. And by doing the will of God, he has greater joy forever in Heaven, for his merits are increased by this choice. By leaving the contemplative life, which is likes, for the active life, which is difficult for him, he gains greater merits, helps more souls avoid Hell, and has greater happiness in heaven.
But he might end up with a short stay in Purgatory, for the aforementioned reasons.
Roman Catholic theologian