The IRS will not send you reminders to file, but you should let them, and your state tax dept, know you have moved and also give them your new address.
I don't think you can file online from abroad as the software needs a US address, but I may be wrong.
Under the US/UK tax treaty any SS payments you receive will be only taxed where you reside, in your case the UK, so your husband's SSDI should be declared on your UK taxes and you should tell the US SSA and the IRS not to withhold tax on your payments. If you get Supplemental Security Income that is not taxable in the US and I believe the treaty keeps any payments that would be tax free in one country tax free in the other too so not tax would be due in the UK either.