If he is wanting to do a complete switch to vaping, it will depend a LOT on the vape he uses too.
I smoke cigs unfortunately. Around a pack a day. So ill give some of my opinions and experience. For over a year now i have vaped and combusted both, most days combusting more than vaping. Ill explain...
When it comes to herb, I get higher from vaping than combusting (when using a good vape) and i use less herb too, both of those reasons are enough to vape over combust.
I do still enjoy the ritual and taste of combusting too though, this makes it harder to do a complete switch, but for me the hardest part of switching from combusting to vaping was finding the right vape that was as convenient as combusting.
Its real easy and quick to pack a bowl and take a few hits off the bong. When it came to vaping (depending on the vape) there is wait/warm up times, and playing with the amount you load, how you grind, and how you hit it to get the ideal vapor production.
The Arizer EQ and Arizer Air i have both got me higher and used less herb than when i combusted... But both came with warm up times and took more time to extract the full amount of noids from the herb.
For instance with the AA, you load a decent load and you can get 2, 10 minute sessions off one load... 20 minutes of vaping or so for full extraction. The same amount of herb that would be smoked in a bowl in less than a minute.
The EQ was similar but had a longer warm up time, and depending on how i used it could take longer or less for full extraction.
This is a good thing sometimes... Not so much other times when im busy doing something else. Or just being lazy. So a lot of times id just smoke a bowl, or a joint... After 15 years of rolling joints i can roll a couple quick Js in a minute..
But now i have an Underdog log vape.... This is just as convenient as a bong for me!! Gets me higher than combusting, uses less herb than combusting or either of my other vapes for that matter... And i can walk up, take a couple quick hits, and go back to work in a minute or 2. Fully extracting the noids in just a couple quick hits.
Since i got it i have not had the urge to combust at home once... And i wasnt even "trying" to stop combusting....
Granted when im out and about, or in the woods for a couple days ill still do a mix of combust/vape... But thats really just because i wont have the log with me.
So IMO it will depend a lot on the vape when it comes to doing a complete switch. But as mentioned before there are plenty good reasons to still vape over combust.