What we know about soft landing is that it exists "for now". It is an undocumented perk and last time someone managed to get Finnair to acknowledge it, it was clear they are not making any promises about it.

There is some kind of grace period too, but unsure exactly the details. For instance, I think you won't earn with tier bonus during the grace. It is more of an "physical card still valid in waiting for new physical card to be sent" so perhaps lounges work. Or maybe they moved on to a real grace, someone else will know