Hugs, Scarlet. I understand why this is so difficult for you--it would be for me as well. I have a few thoughts, some of which I know contradict each other.

First, she says right now that she wants more kids, but plans can change. She (and/or her H) might realize, say, 6 months from now that pregnancy and raising a newborn wiped her out, and she may not want to go through that again. (I know people who initially wanted to have more than one kid, then decided they were done after one.) Or they might see how crazy expensive daycare is (assuming there's no family that would do that) and realize they can't afford another kid. You also mention her being older--so it's possible she may not be able to get pregnant again.

Also, you have a really strong relationship with and connection to L. It could be difficult to find another therapist who offers all she does and with whom you feel a connection. I know when I've searched for other T's when I was having doubts about Dr. T, some said outright that they don't offer email. In fact, there was on who I was considering switching to back in February (I'm glad I worked things out with Dr. T instead), and part of what held me back was that she didn't allow email at all. Or other between-session support, like a call or texting. She said if she had room in her schedule, she could make an earlier appointment, but that was all.

I'm not saying that to be negative about your finding another T who could meet your needs--I'm saying that if all of that is very important to you, it could potentially be worth taking the risk of staying with L (assuming she returns when planned) and seeing what happens. If you find yourself fearing every session that she'll announce her pregnancy, it could be time to move on. Or maybe you just feel too betrayed right now and can't see returning to her at all.

On the other side of things, maybe you could take this time with L on leave to research other therapists. Many offer a free 15-minute consultation, sometimes longer (that one I considered switching to gave me 30 minutes free). Find out what they're willing to offer in terms of outside contact. See if you feel a connection to them. If you're open to virtual, being in such a large state, you'd have plenty of options. If you prefer in person, see who is in a reasonable driving distance. You'd probably have time to meet with a few (depending on their schedules) and see if anyone seems like a potentially good fit.

Someone suggested finding an older T, so you wouldn't need to be concerned about pregnancy. I know you're concerned about retirement, but if you found one who was around 50, say, I doubt they'd be retiring anytime soon and would also be very unlikely to be having a child (though I know it can be possible at that age). Ex-T was in her early 70s when I stopped seeing her, and as far as I know, she is still working, but that may be uncommon.

I hope you can find an answer that works for you. And I'm sorry you're dealing with this.