As long as your visa is still valid and you don't overstay before leaving, there's no issue - you just leave.
The FLR(M) visa is also now more than £1,000 - the visa itself is £811, but there's a mandatory £500 NHS surcharge now, which brings the total to £1,311.
Just be aware though that a US spousal visa for your husband takes a minimum of 6 months, with an average of 8 months, to be processed. They recommend that you start the visa process about 10 months before you wish to move.
If you can qualify for DCF filing so you can apply in the UK, which is a bit faster than the regular processing time if you file from the US, I believe you will need to be here in the UK for that.
You can use a co-sponsor to meet the US visa requirements, so if you have a friend or family member who makes enough to sponsor your husband, you might not need to move back without him to work.
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