They do say that hearing is the last sense to go. When my MIL was at home, before her death at the beginning of December, she was unconscious a lot of the time (partly her condition, and partly the heavy pain medication she was on) but dh and his brother still spent time with her, talking to her, on the basis that she might still be aware, on some level, that they were there with her.
In fact, dh was pottering round the room, setting up his stuff to get on with some work, and wittering gently about what he was doing, when she passed on - and that has been a big comfort to him in the weeks since she passed away.
That said, I do know that it is difficult to see a loved one so ill, and not everyone can - or should - make themselves do it. Ds3, who is 17, last saw his grandmother when she came to visit in the summer, and she was quite frail then - a big change from the last time he had seen her - and he found this very distressing (though he didn't say anything at the time). Later on, when she was admitted to the hospice, she was much frailer and more ill than when she visited, and he decided he couldn't face the thought of seeing her like that, and would prefer to remember her how she'd been the last few times he had seen her.
His older brothers and I did go and visit her in the hospice (which meant ds2 and I flying down from Glasgow - she was in a hospice in Southampton, so it was a big trip). I used to be a nurse, so was not upset by seeing her bedbound and so ill, and the boys did cope well with it - in fact, ds1, who is at university in the South, went to visit her several more times in the hospice and when she was discharged home.
What I am trying to say is that, whilst it was absolutely right for ds1 and ds2 to see their grandmother, and I am sure that they are glad that they did, it was equally right for ds3 to decide he didn't want to see her like that. We did make sure that we offered him the opportunity several more times (she lived for a couple of months after ds1, ds2 and I visited her in the hospice) - I wanted to be sure he didn't regret his decision afterwards, and wanted him to know he could change his mind if he wanted to, and we would facilitate a visit - but he never did, and I am comfortable that he made the right decision for him.
He and his brothers helped dh carry their grandmother into and out of the church, for her funeral, and I have never been more proud of any of them.