Overall, I don't think much would change, but there could be some better continuity flow.
Picture:
Kes helps de-Borg Seven in Sickbay. As a telepath, Kes helps ease Seven's transition from the Hive Mind to hearing only her own voice, by providing some telepathic company. Through this, Kes becomes Seven's first friend on Voyager.
Kes also mentors the Doctor in how to mentor Seven. She encourages Tom and B'Elanna to admit their feelings for each other, based on what she saw in "Before and After," and what she currently sees in their minds.
Her knowledge later from "Before and After" comes into play during "Year of Hell," where she personally saves Janeway and B'Elanna. This leaves Kes conflicted about effectively erasing her daughter and grandson from the timeline.
Her experience with 8472 causes her powers to gradually develop over the course of the season, cumulating in her final evolution at the end of the season. Seven's first friend on Voyager then also becomes the first friend she has to say goodbye to. The loss of Kes causes Seven to become closer to the Doctor and Janeway.