As we know Turbine has made a thing of taking obscure book names, places and characters and fleshing them out. This has definitely been the case for East Rohan, where a number of the Rohirrim are drawn straight from the books. A fair few come from the 'Song of the Mounds of Mundburg', which is in full below:
We heard of the horns in the hills ringing,
the swords shining in the South-kingdom,
Steeds went striding to the Stoningland
as wind in the morning. War was kindled.
There Théoden fell, Thengling mighty,
to his golden halls and green pastures
in the Northern fields never returning,
high lord of the host. Harding and Guthláf,
Dúnhere and Déorwine, doughty Grimbold,
Herefara and Herubrand, Horn and Fastred,
fought and fell there in a far country:
in the Mounds of Mundburg under mould they lie
with their league-fellows, lords of Gondor.
Neither Hirluin the Fair to the hills by the sea,
nor Forlong the old to the flowering vales
ever, to Arnach, to his own country
returned in triumph; nor the tall bowmen,
Derufin and Duilin, to their dark waters,
meres of Morthond under mountain-shadows.
Death in the morning and at day's ending
lords took and lowly. Long now they sleep
under grass in Gondor by the Great River
Grey now as tears, gleaming silver,
red then it rolled, roaring water:
foam dyed with blood flamed at sunset;
as beacons mountains burned at evening;
red fell the dew in Rammas Echor.
Quite a few names here jump out at me, not the least of which is Horn, our recent companion. It's pretty much set in stone here that he will die at some point during the Battle of Pelennor Fields. Some others I noticed are:
Harding; Aldor of the Wold
Deorwine; Betrothed to Winsig
Fastred; Reeve of the Sutcrofts
All in all, not a very pleasant result for the Rohirrim. I am certainly curious as to how Horn's death will affect Nona, if indeed she makes it to that point.