At home, do you have a lot of support from your family? How much physical support can you rely on them for after your new baby is born? Could they come over a few times a week and give you an adult conversation, make you a cup of tea, play with your 3 y/o, hold the baby while you take a shower, help fold laundry, etc, until your body is healed and you are feeling ready to do it (more) solo?
Do your husband and you have good communication and are you in a strong place? Can your relationship withstand the space and the possible feelings that could occur (resentment was one you mentioned)? Can you both put together a bag of tools to help you through any issues or distance that would (potentially) arise? Are you both willing to work through the problems that could come up? Would space be good for your relationship? How much time does he spend at home now, and what hours?
Does he like his work...will he be drained and stressed by it or does he feel better and act like a better partner when he is working?
Do you feel drained or energized (I mean, I know probably both, but generally) being a SAHM?
Does he want to go or does he feel like he should go? Will he feel resentful if he stays?
Is the work dangerous and do you feel worried about him when he is working?
Would you both have access to telephone, cellphone, computer and internet (I'm thinking skype calls)? Would time zones make voice to voice or face to face communication tricky? How might you work around it, if so?
Would he be there when your child is born? Do you have a close friend/family member who could be with you if he is not able? Do you have someone to watch your other little one while you are in labor and recovering/resting afterwards?
Do you have friends who are in similar situations who you could talk to when you were feeling alone, or X?
How desperate are you both for income? Can you survive without? Will you lose your home, your car, or comforts without? How important is that to you both? Are you able to scale down or put buying a house on hold, or is it a priority right now?
How often would he be able to visit?
(When your baby reaches the three month mark), how willing would you be to make the journey with your kids, to visit him once a X and what would the situation be like once you arrived? (I think airplane travel is a lot like car travel...once your used to it and feel comfortable doing it by yourself and with kids, it's not intimidating anymore) How long is the plane ride, what is the climate like where you'd be going and what sort of accommodations would you be able to expect once you arrived (would you have access to a stove, or would it be a hotel room with a microwave)?
I know it's entirely *possible* for one spouse to leave and support the family. It being possible doesn't necessarily make it preferable.
Children do adjust. Of course your eldest would miss him and your youngest might be unfamiliar with him at first. There would be an adjustment period in the beginning, every time there is a visit and when he returned. But they adjust and Love goes a long way.
IF it were me, I would ask myself (and husband) those questions and any I could add. My decision would depend on the answers. I would write up a pro con list, of sorts. I would also take a walk, a bath or a coffee by myself and try to quietly sit with my thoughts and feelings.
Money is hard to come by, so I can see the need/appeal. I can also understand not wanting to be separated. You both will come up with the right decision. Good luck.