Hi Melissa,
I'd suggest replacing the part, as it's my understanding that some of the radio signal functions such as WiFi and BlueTooth may indeed use the case of the phone as part of the antenna, so chances are it may not work correctly without that connection.
Of course, you can always try it out; just reassemble the phone completely but leave out the step where you replace the display adhesive. Then you can see how everything works; if it's fine you just have to pop the screen back off and seal it down with the precut adhesive sheet, but otherwise you will be able to use the phone as is until you've had a chance to order a replacement part and get it installed.
Unfortunately the iPhone XS doesn't have quite as complete a set of guides as does the iPhone X, but I did locate a site in Spain that has one for replacing the WiFi antenna that covers the part you are having trouble with.
Manuales / Apple iPhone Xs / WiFi Antenna - Nadie Me Llama Gallina
As far as getting the part, fortunately you can pick one up right here on iFixit.
iPhone XS Wi-Fi/Bluetooth Antenna
Hopefully that'll get you going again!
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