"Is he still altering chips?"
As far as I know. He has to pay for his food and water somehow

"Are you saying there are more than a handfull of people buying repaired chips and selling them as mint chips?"
No one has ever said that anyone has bought repaired chips and sold them as mint.
It may or may not have happened. If it has then I dont know about it.

"Are they just very high end chips or is this chip repair stuff filtering downword to the lesser expensive chips?"
I know of chips Whalen has repaired which range in value from $20 to $20,000.

"How big of a threat is the chip altering?"
Decide for yourself. Even if Dave had disclosed details of each exact chip fixed, with a scan, we may only be a fraction of the way towards knowing. Dave is a craftsmen. Some of his work cannot be seen with the naked eye. But, he is 'older' and his eyes are not what they used to be. I would not be surprised if some of the people he has taught are better at it than him by now.

"Is this guy the only known repairman out there?"
In Dave Whalens own words.
"I know of 12-15 people repairing chips. I am teaching some of them"

Lets try and put this all into context.
The last time I spoke with him was at the Palms show. He was pleased with the amount of repair business he had picked up. He already had a backlog of 200 repairs before that show.
On one occasion, when I was at his house, he received one phone call and two emails requesting alterations during a two hour time period.

Again, in his own words and those of others
"The list of people who have had chips fixed reads like a who's who of chip collecting"
(he did not mention any names)