It's possible that it won't crack any more, but it's also possible that it will. Mine cracked and then continued to get worse and worse over then next few months until I couldn't drive the truck more than about 10 miles before it lost too much coolant to keep driving it without risking overheating the truck. That's when I stopped using the truck until I could get the engine changed out.

Truth is, if you have the time and money, there is a place in California that can successfully fix cracked engine blocks. I forget the name of the place, but I found it online, so I'm sure you could as well. I almost went that route, but since I'm in NY, from a financial standpoint, it made more sense for me to just replace my engine. Shipping my bare engine block out to them and then back was the main factor in why I couldn't justify the expense. Otherwise, I would have just had my original engine repaired, as there was nothing else wrong with it besides the great big crack in the long coolant port in the side of the block.

Not sure what mileage my Cummins 53 block cracked at. When I bought the truck with 206K, it had already been JB weld puttied up - and poorly - I might add. The former owner was a real douchbag for doing that to me.

Oh, and one more thing... If you plan on doing any modifications to upgrade the performance of the engine, be aware that coolant pressure gets more intense as you turn these Cummins engines up. The extra pressure and flow is likely to cause you even more grief if you have a cracked/patched block. I know that the rear soft plug (aka: freeze plug) at the back of the block is known for rotting away and blowing out under the higher pressures that are created with turning up the engine.

I also know that the rearmost soft plug (a tiny 3/8" one) that is on the corner of the cylinder head just behind the #6 exhaust port is also known for rotting away and leaking. I fixed mine by drilling out the old plug with a very short 3/8" drill bit and a right angle drill... Then tapped the hole with a 7/16" SAE (fine thread) tap and installed a 7/16" SAE cap screw (bolt) with some red threadlocker (loctite) and a copper sealing (crush) washer at the head of the bolt. It worked mint and sure beat removing the cylinder head or trying to drive in a new POS dinky 3/8" soft plug. I'm sure that I'll eventually have to do the same thing to more of them, as there is a 3/8" soft plug found at every cylinder near the cylinder head's exhaust ports.

Finally, the soft plugs that are UNDER the valve cover can also pop out, leading to coolant getting directly into the crankcase and will quickly wipe out your engine by mixing coolant with your engine oil. There are good repair kits to be found online to address this problem, that come with the appropriate pipe tap and pipe plugs to put in place of the POS soft plugs that can fail. There is also a coolant pressure by-pass kit that can be added. Another good kit to install.
I have yet to install either of these 2 kits into my truck, as it's still in stock form and I don't push it that hard. However, it's on my list of "To-Do's" when I get some extra money and time.