Print was king because there was no real alternative. If you circle back to the old issues, you can still be captivated by nostalgia.
However, if you take a critical look to what was actually printed in the mags, there was not much substance. Good photography, hype interviews and some cool stories from the road. Nowadays, stuff like that gets it's minute of shine via social media and it then forgotten.
Skateboarding is not a complex topic, there is little to be written about it month after month, so I see no future for any mag, Thrasher included. However, it will probably survive for long still, but become more advertorial as time progresses.
One thing that mags were and that would still be valuable today is moderators - there was a certain threshold to being featured, whereas everyone is now "self published". I guess print will live on as vinyl does in the music scene - a subculture that puts value in the physical media (however, most skateboarders are some of the cheapest mofos around).