1. Sir, the provisions of ESI Act, 1948 are compulsory in nature and you cannot exercise your option once your wages are out of coverage limit.
2. However, as mentioned by you if you were covered under ESI Act on start of contribution period, then (despite of increase of wages from coverage limit) will continue covered till close of respective contribution period. Therefore, if you were covered in October last year, then will continue covered till March, 2016 (which is close of contribution period). However, you can also check you legibility with the appropriate Branch Office of ESIC to which you are attached. For medical benefit the entitlement will continue upto respective benefit period only.
3. ESI limit is still upto and including Rs.15000/- and nothing has been heard in recent days about any initiatives of appropriate authorities regarding its enhancement.