Illegal importation from legal foreign factories will probably happen, but those foreign factories are going to be building to the same standard regardless, and compared to normal contraband like "plant leaves" it's going to be pretty easy to tell where they are coming from.
Wait, isn't that exactly the problem that's lead to what's happened here? Unregulated THC cartridges causing health issues in states where marijuana is still illegal?
India probably banned both though the article only discusses the former, if so banning the latter is unfortunate since as you note banning it has serious health risks.
By that I mean: I don't think the e-cigarettes themselves are wildly more complicated to produce than the cartridges--though I might be wrong on that.
* https://www.instructables.com/id/Homemade-Vape-Pen-e-cig/
* https://www.instructables.com/id/DIY-Electronic-Cigarette/
* https://hackaday.com/2014/09/13/homemade-e-cigarette-vaporiz...
* https://modern-crafts.net/basics-for-building-your-own-box-m...
Note: mechanical mods are a great way of setting your batteries on fire. Most regulated mods are built around a relatively small number of platforms (https://www.evolvapor.com/), but there's no magic involved and if there aren't open-source hardware now, there will be soon. If you don't care about unit-cost, size, and scale, I'm absolutely sure any electronics hobbyist could build something as functional as most of the commercial platforms.
I can see two obvious consequences of banning e-cigarettes:
1. The Arduino brigade whining loudly that they can't get the parts for their plant-moisture monitor "because you could build an e-cig with that."
2. A rise in trouser explosions from improperly constructed vapes. (Contraband rarely gets UL listed, right?) I would like to officially nominate the term "jake leg" for the resulting limp, in honor of a previous attempt at regulating morality in the name of public health.