Depends what the other discus died of. If it was parasite or bacterial, then I would not introduce it into your tank, unless you do not have any other fish in there. Of course, the only problem is, if you need to use any meds, the meds might effect your plants. Unless you put the discus in a QT tank for awhile.
I would much prefer that the discus go to another person, who keeps other discus and can give good care. I'm not saying you would not be able to take good care of it, but at least, the discus can be with other discus. Discus, do better in groups.
125 gal (473 liter): Low Tech
(1.5wpg PC for 10 hours, no CO2/ferts, gravel substrate), Equipment
(72" Coralife PC, Eheim Pro II 2128 w/built in heater, FilStar XP3 w/Hydor ETH201 inline heater), Fish
(6*Discus, 2*Angel, 5*Clown loaches, 4*L-018 Gold Nugget pleco, 1*L-260 Queen Arabesque pleco, 7*Cories, Farlowella cat)