Ive seen during treatments of patients afflicted with jinns haunting/possession where the jinns recited shahadatain. Whether the jinns really accept Islam or not, it is not for us to determine. Could also probably because the jinns cannot stand the severe pain when ruqyahs are being recited or could also probably be for any other reasons. If the jinns accept Islam with ikhlas and with open heart, may ALLAH swt forgive him/her and give taufiq to always be in the right path. Sometimes, it does not need long bayan to convince the jinns. Other times, take longer time. But hidayah is in the hands of ALLAH swt. Wallaahu a'lam.