I don't think there is a reason to stop using Ike if Roy came back. They're different characters, with different moves. I would like to use Roy in Brawl, but it is impossible to do so. It would be nice to see him with a different moveset, but thats a bit of a pipe dream.
In the Fire Emblem games however, The Sword of Seals fails at trying to be better for the fact that Ragnell has infinite uses.
I was hopping someone would mention something about my post.
Ok, all my info is from
http://serenesforest.net/ and
http://fea.fewiki.net/
Name............... Rng....Wt..........Mt...........Hit......... Crt..........Uses
Sword of Seals..1~2......8..........18 ............95 ..........10...........20
Ragnell ............1~2....20 ........18.............80............5 ........... -
Effects
Sword of Seals: Lord/Master Lord only, Def and Res +5, effective against Mamkutes and Demon Dragons, can be used to recover 30 HP
Ragnell: Ike only, negates Goddess' blessing and non-Wrath criticals, Defence +5
In FE6 attack speed (AS) is determined by
Speed - (Weapon Weight - Constitution)
Roy has 6 con before promotion and gains 2 after making it 8, his sword does not affect him.
In FE9 AS is determined by
Speed - (Weapon Weight - Strength)
Ike averages 17.5 strength at 20/1 and will average 20 at 20/6 so he should not have any problems when he gets his sword.
Mt is the same.
Hit is better for SoS.
Crt is better for SoS.
Uses is better for Ragnell.
Effects, Both get + 5 in Def.
SoS gets + 5 in Res, is effective against Mamkutes and Demon Dragons, and can recover 30HP.
Ragnell negates Goddess' blessing and non-Wrath criticals.
With the + 5 from the SoS in Res magic will not kill as early. The effective against Dragons is very helpful in the last two chapters which are filled with nothing but them and the effect kills the final boss fast. It can also heal you.
With Ragnell, negating Goddess' blessing is not that great with only two bosses it works on and one does not have to be beat, but the other you need it to do anything on him but you could avoid that if your not in hard mode. Ether way Ragnell will be needed for the final boss but it will not take him down nearly as fast as the SoS does to the final boss in FE6. Stoping non-Wrath criticals is really nice, I'll leave it at that. This sword does not heal you, the skill aether does but that skill is unrelated to this sword.
Overall I'd say the SoS is better. Ike is a better character in the FE games though.
Edit: for the uses part, the SoS only being usable for 20 hits is unfortunate but keep in mind that it only has four chapters of use so it does not hurt it too much. Best case scenario you can get 58 uses with the Hammerne. With Ragnell you only get it for two chapters and the BK fight. So even though Ragnell is unlimited it has poorer availability.