Regarding possession by builder

I hv booked a flat at NaviMumbai in May/2015 (Under construction) for residential purpose. I received summons frm court stating that the flat has been alloted to another person prior to my allotment. I was told by builder that he is an investor & has also invested in 14more flats in same building. He has filed a case agaist our builder to deregister my flat & claim to have right over it. I hv compeleted all legal procedures, taxes & almost paid total consideration. The said investor has nothing apart frm allotment letter. On discussion abt this with builder I was told that he has returned all the invested amt & has assured us that he will sort the matter positively. On enquiry of possession he is ready to give the keys inspite of pending works(installation of lights, electrical meter box & lift, water supply, fire NOC, etc.). He is ready to assure us in written to undertake cost of maintenance until the project receives OC. My qstn is considering the above situation should I accept the keys before court case is solved and before recieving OC?