What is the highest level in dnd? etc...

[Olinser]

Because Haley received the sending and had Cloister still had any effect on her than she would not have been able to receive it.

Eh, even the most aggressive estimates of Xykon's power didn't put him anywhere near 47, anyway.

Most people put him in the mid-20's, not very many try to justify him being in the 30s, much less the high 40's.

Honestly, on re-reading, I think the the best estimate comes from Xykon's own mouth:

http://www.giantitp.com/comics/oots0442.html

Xykon seems to think he has about 7-8 levels on Roy, maybe a little more, which would put him about 22-25. (I forget exactly what level Roy was determined to be at that time, I think he was 15).