TL;DR 12.5% of inspired 1 pilots experience fly-away's.
Take this forum and the dji hosted forum and you'll have a good estimate. However, I'd assume only 30-50% of pilots get on the drone forums. A few other pilots I know are more into cinematography and don't post on the drone forums.
I saw a post on here about "400,000" drones being sold by DJI. Assume 80% are phantoms 1-3. Assume 10% are professional kits. That leaves another 10% for i1's, or 40,000. That seems high to me, honestly. At $2900 x 40,000 DJI would have been paid 116 million dollars in i1's alone (gross not net). BUT the company was valued at something like 8 billion dollars recently.
So maybe 116 million in i1's isn't ludicrous.
Also, if 8,000 pilots are on this forum, that's 20% of our assumed total i1 pilots in one place. But not all 8,000 have i1's. lets assume high and say 80% DO have the i1. So the inspired pilots have an assumed total of 6,400 i1's.
In additon, on the DJI inspire 1 forum it doesnt list total user numbers, but it does state 4,000 threads. Inspired Pilots has only 3,000 threads. So lets assume there are 30% more users on the DJI forums. That makes a total of 10,400 users on DJI forums. Albeit, half on DJI are probably also on Inspire Pilots. So the DJI forum has an assumed 5,200 unique users. Again, we assume 80% of them actually have the drones. That leaves us with 4,160 i1's unique to the DJI forum and 6,400 unique drones to the inspired pilots forum.
Totalling 10,560 i1 drones based on assumptions from users on the forums. That means about 25% of the total i1's from our original assumed volume of sales are represented on the forums. I'd say about 50% of the forum users experience failed flights/ fly-away's.
THUS: roughly 1/8 of all i1's experience fly-away's, or 12.5%. Now, this is just a made up number. But it sounds legit. So lets pretend I'm right.