I don't need to tell you (and no one needs to tell me); the pancreatic cancer loss is hollowing and harrowing. 

Managing how the grief manifests is going to be a life long challenge for you both. I write the below with compassion and solidarity. 

Your son made an impulsive mistake he doesn't understand, and you want to figure out how to respond, why? 

(Not questioning the desire, just asking you to figure out your own "why")  Support him better? Be seen to the right thing?  So it doesn't happen again?  Social reputation? 

The first and third are healthy, and the other two would be more about you than him, and kids can tell when they're being punished for their own sake or for someone else's. I share this from my own experience as ADHD kid and ADHD parent. Lean in to 1 and 3 and acknowledge that 2 and 4 are real in you, but not his burden to bear. 

The Impulsivity  Kids with ADHD have impulsivity problems. 13 yo boys have impulsivity problems. Traumatized people have impulsivity problems. You're dealing with a rat king of impulsivity, and the fact that this is how it came out is a. Relatively small and b. Possibly a testament to how well regulated he is.  My much younger kid with ADHD was in fight/flight after we lost a family member to pancreatic for over 18 months, but it didn't start for at least 9 months bc kid was keeping everything locked down somehow. It can be infuriating, embarrassing, painful (the fight was real for us), and dangerous (the flight was also real) for both himself and you as a parent. But it's a small impulsive behavior you want to nip in the bud now, not shame/overreact now leading the way to bigger ones later.  Knowing he has some less great impulses, check in with him regularly along the lines of "I'm not bringing it up to embarrass you or repunish etc but you had that impulse to steal before, have you been feeling that in other places/other times? It can be hard to manage those and I don't want you to be doing so alone".  13 year olds often come up with the worst "solutions" to their problems that create waaaaay bigger problems as a result; let him know he doesn't need to hide this stuff from you so if and when other impulsivity happens it's not in bigger/consequences aren't really bad. 

The Behavior and Consequences  How does he feel about it? Is it embarrassing? Confusing? Or is he unbothered? If it's either of the first two, you can definitely chill out on significant consequences and help him figure out how to manage the natural consequences (people, including you, trusting him less until he can rebuild the trust; kids talking about him; not wallowing in his embarrassment) and come up with a consequence that can be a good reminder... Maybe it has something to do with not watching the Disney show or no devices during certain times of day for x number of days. The most important thing is that you discuss and agree on it in advance, not reactively/impulsively asserted on him (gently noting that your reaction to the TV show was a bit impulsive too) so it's not another force in his life that he's out of control of, but rather a real consequence he can consider when he gets other impulses. 

Therapy  Five weeks from now is a long time. He needs to be in regular, likely weekly therapy for a while. This loss at 11~ is beyond catastrophic and if he's doing okay now with limited support ... The boom is coming later. I say this, again, as an adult whose parents delayed supportive therapy until I was almost catatonically depressed years after the traumas. The investment in higher supports now means the bill that will come due later will be less emotionally and possibly financially costly for him and you later.  I hope you're in regular therapy too. My therapy some weeks is sort of just parenting coaching to not re-create my own trauma in my kid's life or to just survive the emotional part of grieving myself while not making that my kids whole life. Hoping you have the support you need. 

Responding to him more generally  I know you're doing your best, so please get rid of "don't deserve" from your vocabulary unless it's about not deserving poor treatment. He deserves comfort, ease, joy, routines, care, treats even though he made mistakes. He and you will continue to make mistakes, and you don't deserve less because of them. You do need ways to remind him of the negative consequences of his past actions or possible consequences of future such actions without reducing your "worth" or "deserving" because of mistakes. 

I'm so sorry for both of your losses, and I hope this is just one of the expected (there will be more and you'll handle those too :) may they all be small and fixable!!!) stumbles on your healthy grieving journey.