I was not thinking so much in terms of financial difficulty, but in terms of changing company culture. A lot can change at a company in three years. You may have to completely reorient the employee. Or...maybe since the employee has been absent for so long, their position is no longer valued/needed. The company shifts in a different direction without the employee there to shift with it.

Can all jobs be easily replaced with a "temporary employee". If you have a lot of inside knowledge and training that allows you do perform well, it would take a lot of training to get a temp up to speed.

Also, three children may be an "edge case", but two definitely is not and it seems like the same problems would apply.