I like eagleeye's post. It's given me a chuckle.
Whether you repair the one in the car or replace it, you'll be pulling the engine out.
It doesn't take long, like 15-20 minutes to tear an EJ253 apart. Of course, that's with power tools and the engine on a stand. But even without power tools, it won't take long.
I am curious as to how you believe there's a "crack". I've seen plenty of EJs that run hot, blow out a portion of the gasket and a little mill work and new gaskets gets it up and purring. I've even had a couple that had the OE gaskets and the gasket leaked without damaging the block or heads. I will also assume that there's a possibility that when the HGs were replaced last that non MLS gaskets were used, since the MLS tend to hold up to extreme heat and pressure better than the graphite set. Just my experience.
If you take the engine apart you'll be able to determine whether it's usable or not. If the cylinder experienced a detonation strong enough, the cylinder sleeve and block will be blown out, making the engine trash. This would also make it misfire and burn coolant at a great rate if it's running now.
If the engine is losing it at a slow rate, then you most likely will be able to repair it as long as you aren't driving it which would exacerbate the issue. Compression heat and pressure will burn a curf in the aluminum if you run it with a damaged HG long.
As for the valve adjustments, you can get by without it if they were adjusted proper. It's always a good idea to check them though while the covers are off. You will be able to reuse the timing components. I hope you have all new pulleys and tensioner.
You can get reman heads for about $500-600. You can get a whole engine for $1-2k shipped, but then you may have to change the HGs due to oil leak, put on timing components, seals, thermostat, etc. Things you would normally do with a HG job anyway, except you have fairly new parts. (Was the thermostat replaced when the timing kit was done?) You can get a low mileage 2.0L, then you have to swap the intake/harness, cam and crank gear; but these yield less HP than the 2.5.
Until you take it apart, you don't know what you are dealing with. A good sign of a severe blow out is water sitting in the exhaust though, so if you pull the headers and water runs out, it's done.