Defaulting on student loan and sued, renewing green card

No. The only thing that might "affect" the renewal of your green card is the fact that by having stayed out of the country only you know how long, CIS might deem you have in effect "abandoned" your lawful permanent resident status in the US. Once renewal denied and you lose LPR status, it is very hard to obtain a tourist visa, due to your having already had "immigrant intent". The default on your loan will not, however ,have any discernible effect on your ability to renew your green card, but will make it impossible to obtain US citizenship until you take care of that default and reinstate yourself. Student loans are NOT dischargeable in bankruptcy.