There are a lot of German names in Champagne because a lot of Germans with initiative and investment capital flocked to the region as it became Rich & Famous.
Of course they were accepted or rejected by locals based on the way they did business and the way treated the neighbor farmers whose grapes they purchased.
During the 1910 - 11 Champagne riots, not a single life was lost as Moet, Mumm and Piper were burned to the ground and every bottle in their cellars smashed. Bollinger and Roederer were untouched.
When in France in a restaurant, I would order PEEP-er IāD-zeek. I used to know some linguistics, but that was then and this is now.
Piper Heidseick may be a German name, but it is a French Champagne house. However they pronounce it, that is therefore the correct pronunciation. I expect that is the general answer here: Peepehr Idezeek. If you ask for a pronunciation on the internet, thatās what you get.
As long as you pronounce the ārā in the back of your tongue / throat like the French do, youāre OK with Pee-pair Eyed-zeek; but if you donāt, try Pee-pae Eyed-zeek. I would say that Pee-pay is fine also, but Americans tend to make a āeeā sound at the end of āpayā; which is incorrect. Try to get that back of tongue ārā though, like youāre beginning to gargle.