Leave an uncapped pen on a sofa and chances are good the ink gets on the sofa and stains it. If you get ink on your microfiber sofa, there's no need to start hunting for slipcovers. The ink can be removed. Microfiber is a form of polyester. Any stain removal solutions safe for polyester clothing are safe for microfiber sofas. Since you can't just throw a sofa in the washing machine or soak it, spot cleaning is the proper method for removing the stains.
Test your microfiber sofa for colorfastness first by dabbing a bit of either rubbing alcohol or hand sanitizer onto an inconspicuous part of your sofa.
Dampen a portion of the cloth with rubbing alcohol or hand sanitizer.
Rub the stain with the dampened cloth, working from the outside in. When one section of your cloth becomes dark with ink, dampen another section with more rubbing alcohol or hand sanitizer and continue until the ink is removed.
Blot out the rubbing alcohol or hand sanitizer with a dry portion of your cloth or a new cloth.