Since you said you have practical concerns over this, let's look at this from a practical standpoint.
There are 48 guaranteed legends (commanders) per box, plus a few that'll be foils, etc. Chances are pretty high you will find legendary creatures in every color (I'd say it's almost certain to happen). Granted, not every player will see every legendary creature during the draft, but they should see a fair bit, usually enough to find something usable.
But there's always a chance they won't find something. That can happen for one of two reasons, either a player drafted poorly or you got the most color-imbalanced box of Magic cards ever shipped (ie. you got say all green stuff for your non-legendary cards and only blue commanders). Far more likely is draft error or draft stubbornness, ie. sticking with say green because you got one really nice green card but all of the packs coming around don't have any usable green cards, just some nice blue and black stuff (a good indicator you should give up on green and pick up the blue and black shinies, let everyone else fight over and dilute the green among themselves).
And some people are stubborn and will draft to their own detriment or just get ridiculously unlucky and will need a Prismatic Piper. Hopefully since no one will need the full 60 cards they drafted to make a 60 card deck (you will need some lands) and the unlucky player can borrow one. You should expect between 3-5 Pipers to get opened and I highly doubt all of them will get used (if 3-5 people in an 8 player pod need that as a commander, draft mistakes were made or you got a horrible booster box, if people need a 3/3, 5 CMC creature for their 59, they also probably drafted poorly if they can't find better creatures than that). The point here is someone should be able to share. I can't think of any play group I've been a part of where someone wouldn't let another player borrow an unused card for a couple hours.
Finally, in case you get the absolute worst box of Commander Legends ever printed and you need every single Piper you get (or you get none at all and still need one), just proxy it. It's going to be a commander so shouldn't get shuffled in a deck so you can grab one of the advertisement cards and a Sharpie and make a proxy. You'll survive for a couple games of Magic that way.
And if the thought of the remotest possibility that you will need to proxy a card offends you, you can always buy a few online and bring them with you. Right now they cost about $0.10 (USD) so grab a handful and be done worrying about it.
TL/DR: chances are pretty low you will truly need Pipers at all. Chances are even lower that you will need them and not have a spare. Chances are still lower that you will need one, not have one available and can't proxy one or buy a few extra ahead of time. If you get to that point, I don't have any more practical advice I can give you.