> Would subjunctive be either required or possible in Modern Icelandic
> with a sentence like:
>
> Veit Þorsteinn eigi, hvat af honum verðr.
> "Th. didn't know what had happened to him" (or "what could have
> become of him")

The indicative is still normal here.

These sentences would be perfectly normal
(with different meanings):

Þorsteinn veit ekki hvað verður af honum.
Þorsteinn vissi ekki hvað varð af honum.
Þorsteinn vissi ekki hvað yrði af honum.

This one would, I think, be abnormal:

*Þorsteinn veit ekki hvað verði af honum.

> I remember reading somewhere in Old Norse a phrase that meant "come
> what may" or "whatever happens", but unfortunately I can't think
> where at the moment, or what exactly it was--any ideas? I *think*
> it had SEM in it, and maybe HVAT, but definitely VERÐR, rather than
> VERÐI. Could it have been: hvat sem verðr? Google doesn't have
> anything for that though, and I don't know how to do multiple word
> searches on the Orðabók Háskólans' text archive. Sorry to be so
> vague (subjunctive even:)...

I'm not sure what you're thinking of.
I'm reminded of the 'formáli' (rite?
blessing? spell?) from the folklore:

Komi þeir sem koma vilja,
veri þeir sem vera vilja,
fari þeir sem fara vilja,
mér og mínum að meinalausu.

(Loosely:

Come those who would come,
Stay those who would stay,
Go those who would go,
With no harm to me or my own.

The context is usually that of elvish
incursions into a home.)

In this case the subjunctive has a clear
meaning. If we changed 'komi', 'veri' and
'fari' to 'koma', 'eru' and 'fara' it would
turn an expression of a wish or command into
a statement of fact.

Kveðja,
Haukur