Mum was diagnosed with dementia 14 years ago. She is 88 this year. Her food is puréed as swallowing getting worse & sleeps all the time.

Yes, sadly her time may be coming to an end.

Unfortunately likely but only God knows when. I would seek hospice care. Check with your local hospice/palliative care agency to see do they need referral from doctor to evaluate her for services

That is how it was with my dad shortly before he passed. The body is shutting down. Hard as it may be, you must allow it to take it's course. I would refuse a feeding tube and opt to make her as comfortable as possible. It's her time. Tell her it's OK to go. Sometimes they need to hear that. It's said with love. I told my dad over and over that I loved him and it was OK to let go. You have my best wishes.

Often withdrawal from food and bad swallow does indicate end stage, as well as the sleeping. You should now consult with palliative care and hospice after talking to her own physician and see a way forward. Please do not consider liquid feedings. They will prolong suffering and often cause severe diarrhea and bed sores. Do speak with her doctor now and consider hospice so that Mom is kept comfortable. She had lived long with her diagnosis.