Can a bad bedsore lead to sepsis or septicemia?

Yes. Any wound can be a portal for bacteria or other pathogens (fungus), so a bedsore can certainly become infected and the patient can become quite ill, develop septic shock and die or develop associated osteomyelitis (bone infection). Generally these are treated locally and develop no complications.
Bedscore/sepsis. Yes it is possible to have a serious bedsore leading to extreme complications.
Absolutely. Decubitus ulcers (pressure sores) can certainly cause sepsis especially when they become deep and ulcerated. Bacteria can enter the blood stream and cause the sepsis syndrome.
Yes... Any time the skin is open, there is risk of infection. A bad bedsore is certainly a disruption of skin integrity so bacteria can then enter and infect the wound. Since the wound has a blood supply, the bacteria could then enter the blood stream thus transporting the bacteria to multiple organs leading to sepsis.
Yes. Any break in the skin can allow bacteria to enter the blood stream. As the bacteria multiply and cause signs of infection this is referred to as septicemia/sepsis. Bedsores often occur on bony prominences around the patient's buttocks. This area is particularly prone to contamination with colon bacteria that can cause sepsis.
Yes. . Bad Bacteria thrive on dead tissue, blood and a lack of oxygen. All these things are present in a bad bedsore. .