Once guys like Harpur and Schmaltz were sent down. Ice time for the kids was going to be limited. I think Keefe has done a good job balancing it out. Lindgren is one example.
The defense is not a problem.
Sandin and Liljegren play every day, and Lindgren/Rubins are 97's with at least one usually in the lineup. Our "old guys" are Gravel, Schmaltz, Harpur and Kivihalme, all of which could still have some future usefulness for the Leafs at some point. They usually try to make the defense at least half prospects and half guys with some experience. They are actually doing a good job at keeping guys with usefulness in there at all times... Which is probably why they never used and eventually traded Ryan Johnston.
I think if the Leafs move Marincin, they will call up either Gravel or Schmaltz to be the new #7. At that point, we may see Hollowell or Duszak if they are okay with them playing in a rotation this year. Otherwise, they'll probably call up Kapla or Gudbranson and get someone with a bit more experience.
Forward is likely what people are more concerned about, but at the same time Marchment and Kossila will eventually come back and at best I think Luchuk and Conrad are the only ones worth playing over guys like Read and O'Brien.