You aren't taking what he said seriously. The junior could also get sick, present management issues, etc.
If this person plus a junior represented "1.3 engineering knots," he's saying... "actually, I'm still 1.3 engineering knots without him."
When this person leaves, they go find someone else who is 1.3 engineering knots. The junior represented .3, without the 1., it doesn't matter that much. Headcount strategy shifts.