No, the sealing is still there as the sinner is lead to confession. Your confusion is natural for someone who does not believe in the free will, but for a Catholic mind the seal opens up particular graces given to a baptised Christian, confirmed Christian and ordained Christian, but it does not sheld them from temptation. Which brings me to this general question, why pray Our Father at all given the understanding of Perseverance that excludes the free will?
Since many Catholics do not actually practice confession who have been properly Baptized, the Spirit is of little value for salvation, in His own right, since everything depends on free will. Also look at His track record, under the Catholic view, if the Spirit advises all people toward God. Pretty weak.
So all the verses that talk about being sealed on a permanent basis really don't mean what they say, they mean on a temporary basis. No one is therefore actually sealed. In Catholicism it is much more like a Ziploc bag. Open, shut, open, shut.
... why pray Our Father at all given the understanding of Perseverance that excludes the free will?
God commands us to pray and if it's good enough for Jesus it's good enough for me. There are a million subjects of legitimate prayer that do not directly impact on actual salvation. Moreover, I could turn it around and ask why would you pray to God, since God will not touch man's free will and everything, including the ultimate salvation decision, is man's free will.