Currently (Feb 2013), we have about 50000 tx per day, or 0.579 tx per second (tps), or 347 tx per block (tpb). We are paying miners 25 BTC per block, or $500 per block at current rate. If bitcoin becomes the VISA scale, it has to handle 4000 tps, or 2400000 tpb, or 6916x of the current volume. To keep mining profitable, we may need to pay $50000 per block (to pay electricity, harddrive space, bandwidth, CPU time for ECDSA). As the block reward will become 0 in the future, this $50000 has to be covered by fee. Since we will have 2400000 tpb, each tx will pay $0.021, not too bad when you can send unlimited amount of money to anywhere in the world in no time.
That means mining is profitable even without any block size limit.
On the other hand, the 1MB constraint will certainly kill bitcoin. 1MB is only about 2500 tpb, or 0.1% of VISA scale. We are already at 13.9% of this limit. If we don't act before problem arises, people will start migrating to alt-coins.
Let's assume a miner with moderate hashing power can mine 1 in 10000 blocks (i.e. one block in 10 weeks). With $50000/block, he will get about $5/block.
2500000tpb (VISA scale) means about 1GB/block. Currently a 2000GB drive costs about $100, or $0.05/GB. Therefore, the harddrive cost is only 1% of his mining income. It's negligible. (and harddrive will be much cheaper in the future)
A quad-core Intel core i7 is able to handle 4000tps (
https://en.bitcoin.it/wiki/Scalability#CPU) at 77W. Assuming $0.15/kWh, it costs about $0.012/h, or $0.002/block. Even energy is 10x more expensive in the future, it's still negligible. (and CPU will be much efficient in the future)
1GB/block needs a bandwidth of 4.3TB/month. Including all overhead it may take 10TB/month, and may cost $300/month currently for a dedicated server in datacentre. It is $300/(30*24*6) = 0.069/block. Again, it is negligible comparing with the $5/block reward.
He will still earn $5-0.05-0.002-0.069 = $4.879/block after deducting the harddrive, CPU, and bandwidth cost. It is $29/hr or $21077/month and is a ridiculous amount given he only owns 0.01% of total hashing power. He still needs to pay for the electricity bill for the mining equipment. It is hard to estimate but even if he uses 90% of the earning for the electricity bill, he will still earn $2107/month.