That's about the gist of it. Omoi is more like feeling, emotion, thought ... todokeru I would say is "reach you". So something like "Until how long will this (dear) feeling/emotion reach you." It can be really hard to translate Japanese to English as so much is implied rather than stated, and we don't spill out everything in words.
この思いは いつまで あなたに 届けることが できるのだろう。
