1. Check the conditions of abstract submission - I've seen conferences that specifically state that abstracts won't be accepted if they are based on work already submitted for publication, or proposed in the same form to other conferences (i.e. presentation/poster etc.). Some won't have this caveat however.

2. Peers of mine have submitted abstracts with 'results so far' sections. If you have no results to state in the abstract, they may provisionally accept you until you can update them on your findings. I suppose they may be concerned that you won't get them by the conference date, in which case they may think it safer to decline.

You need to check with your research council's term and conditions/guidelines. I know that many research councils will also expect you to repay any over-payment you've received for the year if you do leave early.