My dh was gone for four months during the past year- I had a 3yo and a 1yo. It was tough at first... but once we got in a good groove, it was nice in some ways. Simple meals, our own schedules, and... KNOWING nobody was coming to rescue me at 6pm made a difference in my mindset. So I just let go, and did the best I could. We had a great time, actually. Knowing it was just the three of us, we did fun stuff, went to see friends, did a lot of kid-friendly stuff... following our own schedule. And the experience made me stronger as a mama, knowing I could do it by myself, and now I find myself a bit more confident and comfortable in my parenting. Which helps because my dh works crazy hours and we don't see him very much these days.
But what helped....
I really stuck to a strict dinner/dishes/bedtime schedule. I still do, actually, since dh works nights. We have dinner from 4-5, and I always do dishes RIGHT after dinner, no matter what- the kitchen is clean every night. The girls are always asleep around 8pm, sometimes earlier. This is what saves my sanity. Nighttime is when I have time to myself. For baths, internet, talking on the phone, reading, crafting, whatever.
Make the house as safe and child-friendly as possible, so you don;t have to be super-super vigilant on watching the kids. Make it totally safe, as much as possible, so you are free to do things in other rooms and check in on the kids occassionally.
Having great carriers- when dh was gone, I bought myself a mei tai and a wrap. When I was comfortably able to carry my babe on my back- I could be more free to play with my older girl. We could go out to town or take hikes and have fun!