I lost the remote and cannot remove the PIP.

Hi, I have the same TV, remote too. From what I can see you will need the remote to turn off the PIP, but if you unplug the TV and the plug it in again it may reset it to original values. As long as it is plugged it will retain certain low power settings.
If your Comcast remote is a learning remote, you can probably program it to mimic/replace the remote you lost, but you will need the codes from the Sony remote, or borrow one so the codes can be "learned" by the Comcast or some other learning remote. The codes would likely be available online, from Sony.
Worst case - I'll buy for you a cheap learning remote and dump the codes from mine if you want.

Also, you may find a used remote on line.