I'd be pleased that S&W was able to get Walther to agree to replace the gun at no cost. Be patient.
I've known of 2 SW99's and a P99 which experienced some ammunition-related problems.
1 SW999 (9mm) had a case head failure/blowout which not only cracked the frame but blew out the right side above the shooter's hand. They examined the gun and replaced the frame under warranty (the slide & barrel weren't found to be damaged).
A LE SW9940 experienced what was determined to be a squib load which was unnoticed by the shooter during training. An obstructed bore resulted in an unnoticed crack in the frame. The crack was eventually discovered because the frame flexed under recoil and kept pinching the shooter's hand. S&W replaced the frame under warranty.
A P99 (forget the caliber) experienced a squib load and a "ringed" barrel. No damage to the frame or slide. S&W replaced the barrel.
Another P99 (9MM?) owner had his slide break off at a corner of the rear dovetail (the rear of the slide separating from the rest of the slide, as it was described to me). The gun had reportedly been fired for several thousand rounds over the course of several years. Walther declined replacing the slide due to the gun being out of warranty and apparently did not consider the slide to be defective. S&W offered the owner a new P99 titanium nitride treated slide they had on hand (for whatever reason) in the repair center at no charge and the owner agreed. He was pleased with S&W's response and good will gesture last I heard from him.
Now, the guy who had his SW999 frame damaged by the casehead blowout? He told me he's since fired approx 55K+ rounds through the gun since then. He has a SW9940 through which he's also fired more than 55K rounds. I had to replace a sear housing block because of a broken ejector in the gun at over 50K rounds ... and since it was a SW99, S&W covered the replacement block and sent it to me (as an armorer) under their lifetime warranty, even though it was a Walther part (and has a retail cost of about $100, BTW). Last I heard he's still firing a LOT of rounds through his SW99's ... and I just keep him recoil spring assemblies, mag springs and I recently replaced his striker springs.
Back before the M&P pistol series was released, and the SW99/990L's were still being produced and sold, I was told that S&W kept a SW9940 at their training academy which was used for testing & as an in-house loaner. I was told at that time that it had been logged as having fired more than 75K rounds, and since it was essentially kept as a test gun it had received no cleaning or other maintenance in all the time it had been in use. Yes, that's intentionally abusive, but the fellow who told me about it said they were interested in seeing how it withstood the extended shooting under lack of proper maintenance/abuse. As an armorer I'd not subject a gun to those conditions ... and especially not one dedicated to defensive use.
Now, I've fired several thousands of rounds spread among a number of SW9940's, since I carried an issued one for a few years, helped maintain over 50 others during that time and own one of my own. I've had to replace a few of the Walther parts, some of which seemed to be caused by user abuse and damage. I did have to replace a couple or three sear housing blocks for broken ejectors.
I've fired more than 10,000 rounds through a personally-owned SW999c. It had an occasional light strike issue on the DA trigger stroke when new, but after consulting with a tech at Walther America who said he had occasionally seen it happen in the P99 line, I was able to correct the problem. That was several thousand rounds ago and the problem has never reoccurred. BTW, I really like my SW999c.
I think the 99 series is a fine design which never really received the attention it deserved. I've always wondered why Walther never seemed to demonstrate much interest in really promoting & advertising the line in this country, although I've been told they've focused a lot of attention on promoting the 99 series to LE/Gov outside this country.
I did learn of a revision to the Walther frames at one point when I found a replacement sear block wouldn't fit in an older SW99 frame unless I switched a housing pin from the old block to the new one. The housing blocks appeared different in dimension, too. When I called and asked S&W about the difference between the blocks they confirmed I could replace the bottom pin to make the new housing fit in the old-style 99 frame, but they said they couldn't tell me why Walther had made the change in the frame. FWIW, the sear housing block is located to the rear of the magazine well, unlike where the crack is displayed in the OP's 99 frame. It might be fair to remember that firearm manufacturers are often making revisions to things for reasons which make sense to them.
Sorry to hear you're having to wait quite a while, but enjoy the new P99 when it finally arrives. Fine pistol in my humble opinion.