No, no, the buffs stay for the whole duration.

If in round1 you copy an MB with root of warrior and swordbearer buff you get for two rounds root of warrior and for 5 rounds swordbearer buff. If the clone or yagura die the buff stay for the whole duration unless they are dispelled. rFor example, with azure fang, in arena, i use to copy a ton of times mbs with root of warrior and even if the clone or yagura die in the 1st round my azure fang continue to be immune to all debuffs also in the following round.

If in round 4 you copy again the same mb you simply get the buffs refreshed, if you, instead, lets say, copy a mifune you still have the swordbearer buff from mb for round 4 and 5 and you get ALSO mifune buff for round 4-8.

Your impression is right, if a buff is casted for x round it stays active wholly for their duration, regardless the fact the ninja providing it died and only a dispelling effect, like han or cee or temari gnw mystery can remove them before their expiring time. What cease to work the moment the ninja providing it dies are auras and barriers. Things like healing tips or wb asuma passive or anbu special tactics leaching effect, to be clearer.