I do still draw a line on a chart.
You can even print the pre-drawn lines out of SkyDemon, on the charts, as well as include the weather, plog, weight & balance, fuel calculations... etc... Everything you may need along the way, even including your aerodrome plates, as well as your alternates in a nice "package" by tapping the button "Generate Briefing Pack". In which case you won't ever need to buy real maps ever again!
The only thing I can't yet do is get IFR charts at the same time - that's when I use autorouter to generate the same path with GRAMET, and IFR charts.
What if you iPad has all your plates on it, but also SkyDemon or equivalent?
EasyJet now does this on all commercial routes (the plates bit). But they do have means to plug in the iPads in the plane, and have spare battery pack(s) in addition to 2 separate backup iPads. But I've been told that the likelihood of 2 iPads failing / breaking / running out of battery was highly unlikely.
I would ALWAYS have a paper copy of the charts / plates (just in case). Also for planning its really useful when in unfamiliar territory to have a slightly broader picture of what is around in paper form. Especially if you can't divert to your alternate(s), and need to pick a new airport to go to.
Even the most basic of smartphones now has a GPS/maps function.
True - but if you're flying at 5,000' you are unlikely get any reception to download the map. A blue dot on your location is a good idea - but only when you have a map to overlay it on! Also be wary of the accuracy of the blue dot, I sometimes find myself several miles / occasionally hundreds of miles away from my actual location.