It's an awful situation to be in and good to hear that the safeguarding issues will actually be looked into. In my Mum’s case, having raised safeguarding concerns with regards her hospital treatment/care, the safeguarding team simply replied that they “were not involved in hospital care management” and didn't want to know the details..
From personal experience, PALS were happy to listen to and try to address concerns raised when Mum was a patient but when concerns had still not been addressed on discharge they didn't want to know. It seems that once someone has left the hospital PALS responsibility ends. For info, they never asked me if I had H&W POA but maybe other PALS teams do.
with no report of the treatment received during his hospital stay.
If you mean that your father in law or the care home were not provided with a discharge letter then I would try contacting PALS to request a copy of this. They may be willing to provide this as hospitals are required to provide these on discharge. Rather than 'complain' about a discharge letter not being issued just let them know that this wasn't provided to the care home/relatives when your father in law was discharged so could they please provide a copy as it is needed to assist with his care plan. From personal experience discharge letters can vary in standard, can contain very little information about care/treatment provided and can sometimes be inaccurate so it may not help you much but you could at least try to obtain a copy.
If you want to go down the route of requesting the hospital records check the hospital website for details about their process. When I did this the process was quite simple. There was a data request form to complete and if you apply on behalf of someone else you just need to provide their written permission (and their ID) – a typed letter which your father in law has signed would be sufficient, providing he is able to do this. Good luck , and I hope that your father in law is recovering from his ordeal.