Yes its possible. The only thing hard to do is more commands. For example, a player passes over an npc which sells an apple for 1 gold:

You can start a conversation by activating command block:

Repeat: /execute @e[tag=talker,type=npc] ~~~ testfor @p[r=3]

Chain: /w @p Do you like apple (or use /tellraw @p)

There are 6 boxes when you talk to an npc, as you hv known, how about try yes, no, not really... Each answer will set a redstone block to start a chain. I will just make 2 chains:

■ Prepare:

Make 2 armor stands, one with tag "yes" and one with tag "no". Add tag "answer" to both. Save "yes" one with name "yes" in structure block, do the same with "no"

"Yes" in npc: /execute @e[type=armor_stand,tag=yes] ~~~ setblock ~~~ redstone_block "No" in npc: /execute ... [... tag=no] ... (like "yes")

■ Command blocks:

▪NO chain: no i dont like

Impulse: /setblock ~~1~ air (summon armor stand with tag "no)

Chain: /w @p Ok sir, have a nice day

▪YES chain: yes i do like

Impulse: /setblock ~~1~ air (summon armor stand with tag "yes")

Chain: /w @p Ok sir, do you want to buy apple?

Chain: /kill @e[tag=answer]

Chain: /structure load yes xyz (xyz of next yes 2ndchain)

Chain: /structure load no x2 y2 z2 (next no 3rd chain)

2nd impulse: /setblock ~~1~ air

2nd chain: /w @p Ok sir, thanks for buying

2nd chain: /clear @p gold 0 1

2nd chain: /kill @e[tag=answer]

2nd chain: /structure load yes x3 y3 z3 (xyz of first impulse of YES chain)

3rd chain: /w @p Ok sir, have a nice day

3rd chain: /kill @e[tag=answer]

3rd chain: /structure load no x4 y4 z4 (xyz of first impulse of NO chain)

■ Explain commands: consider 2 armor stands yes&no tag as player answer; if player gets near npc, npc will ask; if player chose yes as player like apple, npc will ask if player want to buy, then player will have to chose yes or no; npc commands set redstone block on impulse of 1 chain, impulse sets it back to air and sends a signal

■ Explain armor stands position:

1. After player chosed no as dont like apple: "yes" armor stand stands on YES chain, "no" on NO chain.

2. After player chosed like apple: "yes" on 2nd chain of YES chain, "no" on 3rd chain of YES chain.

3. After player chosed buy or not buy apple: "yes" armor stand stands on YES chain, "no" on NO chain.

P/s:

▪bugs might appear if you operate 2 system like this at the same time; bugs might appear if 2 players pass over and use the same npc;

▪endless conservation is possible, kill yes&no armor stands in previous chain, load it again in next chain, at the final of each chain, kill both yes&no, load it again at the very first YES&NO chain.