You make it sound like IKEA isn't fit for second hand use. I live in Scandinavia, the classifieds and the second hand furniture shops that do not specifically cater to the vintage crowd, says otherwise. There's a
lot of IKEA furniture on the second hand market. Of course it gets second hand use. And if you are in a university city, you can bet that a lot of the furniture students have is on its third or fourth owner.
As for "ecological lifecycle", that's a more complex question than can be expressed in a few paragraphs because one needs to understand what timber is and where it comes from. As well as how it is used.
If this genuinely is a worry of yours then I'd be more worried about what to eat, since the deforestation that actually matters, that of untouched virgin forest, is mostly to produce what ends up on your plate. Mostly beef, but also oil crops etc. The timber in your furniture comes from managed forests. Essentially crops. Of which there is no shortage.
However, there is a shortage of virgin forest. In Europe genuinely untouched forest, which is the kind that matters for biodiversity, is somewhere in the region of 2%. Which is why most Europeans will never see actual virgin forest during their lifetime. The thing they think of as forest is managed plantation with low biological diversity.
(The situation in the US isn't nearly as bad as in Europe. Alaska has mostly virgin forest for instance)
This is why countering deforestation isn't about "just planting trees". If it were about that we wouldn't have a problem because we plant orders of magnitude more trees than we fell in virgin forests. In the US alone about 1.2-1.3 billion seedlings are planted yearly during the planting season. To maintain an equilibrium.
Where I live he amount timber, by volume, has tripled in the past century. The problem isn't that we have too few trees - it is that we are behind on managing their age distribution. 40-45% of the forest where I live is harvest ready. About 10-15% of it is overdue.
(And we haven't even touched on recycling, and the amount of recycled materials found in the products of IKEA and others. Of course, if one has romantic notions of solid wood furniture then one would most likely sneer at products made from recycled wood)