Banner of the World Dragon..-workaround ...tips and tricks

How do Daemon players cope with the Banner of the Crutch Dragon? By playing a different army against HE wherever possible, or shaming the HE player into not using it against Daemons.

Basically you've already answered your own question. BotWD is a hard counter to Daemons, and all you can realistically do is avoid that block while 'six' spelling it to death.

How about asking your opponent not to use it when playing friendly games with daemons of chaos? Feels like HE has a lot of power stuff anyway.

It's not a tactical solution but a way to make a friendly game fun for both parties. Of course not possible for tourneys or people you face the first time.

Maybe he can roll a dice and a 50/50 don't use it. Makes you wonder in the dark and need to play around/test for it.

Or you can set your mindset on crazy stuff/beating the impossible and celebrate like hell when on an occasion you win.

It depends. With Daemons it is very hard to counter, but one of the best counters is simply to not fight that unit in combat. Of course this is easier said than done, but throwing a handful of single Beast of Nurgle units towards that block could keep it tied up for a very very long time, if you destroy the rest of the HE army you win by points. That option is harder to do if your opponent runs a Cavalry Bus with good board control, though.
Another extremely important question is where is your opponent bringing it? If they have it on their BSB then it is much less of an issue. On a unit standard bearer and it's very tough, but on a BSB that BSB at the very ultimate best has a 2+ armor to go with that ward and 2 wounds with no magic equipment. In that case, force your opponent to roll the dice. T3 is super easy to wound, the more hits you get the more saves they have to make and a few always go through.
Something else that really is just ignorance on my part, but are Daemon impact hits magical? If not then Chariot impact hits will rip through any High Elf unit very quickly.
Another option is to use your own magical debuffs to hit the BotWD unit so they are severely nerfed then hit them with a block of Plague Bearers or something. Turn it into a fight that never ends between two opponents that cannot hurt each other.

All in all my number one bit of advice is to just avoid the unit and try to kill the rest of the army. If that cannot be avoided then send in something that makes the High Elves roll a huge number of saves. Hard hits aren't necessarily the option, when you're trying to make an opponent fail a 2++ you want them to roll a ridiculous number of dice. I've had a similar fight where I was using the 3++ Phoenix Guard build and in one battle they steamrolled my opponent's Empire Inner Circle Knights because the Knights had some good S5 attacks on the charge but there just weren't many of them and my 3++ didn't care about the S5. In my other battle the Guard were overwhelmed by 2 units of Skaven Slaves and a unit of Clanrats pushing the Bell. I was just rolling so many dice that the Guard were worn down. I took more than half the rats with me and it lasted around 5 rounds of CC, but in the end I lost and the destruction of that unit cost me the game.