Rank inactivity still accounts?

Yes and no.

You can still get demoted. Getting demoted for inactivity has no impact on MMR. Ranking has no impact on initial seeding, only MMR does.

They haven't made an official announcement, but last season they turned off decay during the preseason period.

NOTE THAT the preseason period starts NEXT PATCH, NOT RIGHT AFTER THE CURRENT SEASON ENDS. So currently you can still decay. If they do what they did last season (and I don't see any reason why they wouldn't), they will make an announcement soon and stop decay when the next patch goes in.

Since that last patch was not too long ago, I'm guessing we have a few weeks til the next patch (beyond 9 days), so I would recommend getting a ranked game in soon to reset the decay period.