I believe you have made a right choice. Hope you mum gets well soon, so that you would be able to come to the US with H4 visa, in the next a few months.
You could file your 485 as a dependent of the primary applicant (you hu*****and) right after coming back, as long as his 485 is not approved by then, which I strongly believe so due to the vast amount of 485 cases in these 2 months.