So with the extreme cold in chicago this winter, we have somehow destroyed the undercarriage panel on our S type. We heard a dragging sound, so I zip-tied the under panel temporarily. However, my wife backed over some ice, or caught a curb just right and the under carriage panel is mostly missing.
(not blaming her, mad at myself for not taking somewhere sooner)

Are there instruments or mechanics under the S type that will suffer from having more exposure to the elements? Is this a must-replace item, or a should replace item.. or a maybe replace item?

How bad is this?

 

I have a 2004 S-Type, very similar to yours. I have had the undertray off/on several times doing oil changes and have asked myself the same question. I decided to leave it on because the alternator and A/C compressor are down low and vulnerable to road splash. You can imagine what a good dose of salty winter splash would do to an alternator. I live in Florida and don't have to deal with the winter weather, but do get a lot of standing water on the roads. I would recommend replacing your undertray. You may be able to get a used one from Coventry West in the the Atlanta area. They have a dedicated Jaguar junk yard. Good Luck.

 

It probably provides some protection and may improve mpg. If you can cheaply get another (wreckers?) I'd fit one but otherwise... I don't know.

 

I would consider it as added protection.

However, I would also want to note that my Volvo and previous BMW never had one....

 

I don't like the inconvenience of having to remove/replace the belly pan for oil & filter changes but as others have said, there is so much low-hanging fruit down there that would be very expensive to have to replace (especially the compressor). It only takes one wayward flap of a blown-out truck tire flying around down there at highway speeds to take out some very costly components. That thought alone causes me to keep the belly pan in place....

 

+1 on what the others said but if mine got trashed and it was going to cost $$$ to replace I'd have to give it some serious thought but I don't have to contend with snow and ice :-)
Without the panel your wife may have caught a power steering or transmission cooler line with a lump of ice!