No. It'd be an incredibly difficult life with no guarantee that it'd work out for them. Read what I wrote above if you want my reasoning. Basically, they're going to be illegal immigrants and fugitives hiding in a country where they don't know a single other person or speak the native language. Shio would be much better off in a Japanese orphanage.
When you bet to win, you risk to lose.
That's an universal law.
When you try to achieve something, there's always a risk of failure.
Things are never entirely under your control.
That's because, in life, there's always a risk of shit happening.
That's why it's kind of pointless to tell someone who's betting big in order to win big that they risk to lose. They already know. Instead, you should applaud their courage and cheer for them. After all, most people in the world tend to avoid risks whenever they can, even if that means wasting any chance they could have had to get the things they really want.
In this case, there are risks in living as illegal immigrants in a foreign country where they'll have to speak English, not Japanese. But it can be done. You say it'd be better to send Shio to an orphanage, but do you know orphanages have always been pedophile magnets? There's a real risk that Shio would end up in the newspapers as part of a story about children raped by their caretakers. In all honesty, I much prefer having her at Satou's side and knowing she will be well protected. Life out of Japan won't be easy, but I'm sure they can manage. After all, if a couple million fellas are living as illegal immigrants in the USA and doing just fine, hell, Satou and her sweetie can do it too.