Does a low profit margin on mining reduce the integrity of the blocks stored in the transaction history? As the mining Bitcoin payout decreases from 50 to zero, what incentive is there for miners to continue operating?

Is there a need for miners to continue to operate when the payout decreases to zero?

I thought part of the purpose of mining is to validate the Public key with the General Ledger that is replicated in P2P fashion between nodes.  If the miners go away, will GL validation stop?
All that is needed is a number of miners sufficient so that a consensus of bad actors gains control to disrupt the blockchain doesn't happen.

Transaction fees are a tiny fraction of the level of the block reward subsidy ( still not exceeding 1% ) but as bitcoin is more widely used, the fees will eventually make up for the lowered subsidy.  That's what is expected, and so far that appears to be what is actually happening:


http://blockchain.info/charts/transaction-fees?timespan=180days&amp;daysAverageString=7