I don't think the digestive system will give you much usable B12.

B12 deficiency is common long term. It may bounce around but mine finally settled after 3 years. B1 I had to go with weekly injections for 4 weeks but it's been fine for a couple of years now. I believe the B1 deficiency that affects nerves the most caused issues with the vagus that ended up with a diagnosis of dysautonomia or completely out of whack autonomic nervous system. Much like what you're experiencing with the cardiovascular system I also experienced in almost every autonomic system in the body including heart rate, blood pressure, digestion, swallowing, breathing, hormone loops out of balance and even a large amount of muscle atrophy head to toe. I believe the muscle loss is from cardiovascular deficiencies.

I've been aspirating for quite some time also. All the increased secretions from the lungs trying to fix that has almost destroyed the lungs like advanced stage COPD. They wouldn't consider a feeding tube because my lung capacity was too low for surgery and my overall condition wasn't good enough back in the fall of 2012.

This all began back in about 2009 or 6 years out.

SCC Stage IV, BOT, T2N2bM0
Cisplatin/5FU x 3, 40 days radiation
Diagnosis 07/21/03 tx completed 10/08/03
Post Radiation Lower Motor Neuron Syndrome 3/08.
Cervical Spinal Stenosis 01/11
Cervical Myelitis 09/12
Thoracic Paraplegia 10/12
Dysautonomia 11/12
Hospice care 09/12-01/13.
COPD 01/14
Intermittent CHF 6/15
Feeding tube NPO 03/16
VFI 12/2016
ORN 12/2017
Cardiac Event 06/2018
Bilateral VFI 01/2021
Thoracotomy Bilobectomy 01/2022
Bilateral VFI 05/2022
Total Laryngectomy 01/2023