Math question about the health regen changes...

I don't think so... because the percentage ones was the BASE... and seals give BONUS not BASE... so maybe the formula like this...

(BASE * %) + BONUS

BONUS = Runes, Masteries... or anything that states as BONUS regen in items... (like Doran Shield or Doran Ring)

You should only ever use Health or Armor for your seals honestly

Mostly this was a neutral move for Health Regen. Even the lowest Regen value in the game (Gnar) gets more out of Bead of Rejuvenation at level 18 (5.5 HP/5 vs. 5 HP/5), but only one character gets more at level 1 (Heimerdinger; 5.5 HP/5 vs. 5 HP/5). Before, early game is all regeneration was good for, and now that's shifted to be much more useful lategame, at least somewhat.

However, though Beads are highly buffed in lategame, many higher items were nerfed to compensate. The highest Regen on an item aside Warmog's was 24 (Spirit Visage). Now, with it at 100% HP Regen, only about 1/3 of all champions ever reach that usefulness of Health Regen at level 18, and if before level 18, the rate drops fast. Generally, if Health Regeneration is a priority to you, you want to upgrade lategame now. For this reason, champions can cheaply get fairly high Regeneration in the midgame area with Beads, and then get loads of damage elsewhere, and finally upgrade the Regeneration items as necessary, when space enforces it mostly.

And what does this say for Runes? Well, if you depended on Regen earlygame before, you may need flat Regen runes more than ever now for the early levels, but you can depend on your enemy having less Regen sustain early as well, so there's a trade-off there. Lategame, if your champion needed high Regen bonuses to stay alive before, they probably need it more than ever now, and Regen/lvl runes might be in order instead of Regen items. Midgame, though, Beads are pretty much the way to go, so all in all, I'd say for the minimal boosts in early/late game Rune usage, the midgame is going to be dominated much more by cheap Bead Regen, and therefore drop the value on Health Regen Runes.