Political pundits are certain the draft charter is doomed and will derail the roadmap, enabling the regime to continue its rule and postpone the new poll until a new charter is in place.
According to the roadmap, the new general election will be held next August if - and that is a big "if" - if the charter is approved by the National Reform Council (NRC) and the referendum.
Prime Minister Prayut Chan-o-cha would remain in his position for only two more months after the election when the new cabinet is installed and royally endorsed.
Meanwhile, the NRC will come to an end whether the draft charter is approved or not.
It will be replaced by a National Reform Steering assembly, to be hand-picked by the military regime. But this new body will be dissolved once the new parliament begins operating.
As for the National Legislative Assembly (NLA), its term will end once the election and selection of senators is complete, Mr Wissanu said.
The Charter Drafting Committee (CDC) will be dissolved when the new parliament is in session, he said.
Mr Wissanu also gave a clear-cut political calendar for these changes. The organic laws will be drafted by the CDC and the NRC in January 2016 and sent to the NLA for deliberation during March and April, he said.
Some have doubts, however, that the drafting of organic laws will be completed according to this timeline.
When completed, these organic laws will be forwarded to the Constitutional Court in May for endorsement. It will take 90 days to prepare for the election expected to be held in August next year.
The announcement of the general election will take 30 days, and then the royal inauguration of the new parliament, the appointment of the new prime minister and the new cabinet, to be capped off by the royal audience, will take place.
The whole process is expected to be complete by early October next year, the deputy prime minister said.
But if the draft charter does not pass the referendum, the scenario will be different, he said. And that is exactly what many political pundits believe will be the case.
Their belief is cemented by several recent events. It started with NRC member Wanchai Sornsiri's loud opposition to the draft charter and renewed "reform-before-election" campaign.
He claimed a large number of NRC members would vote down the draft charter so Gen Prayut could stay on in power and effect reform before the poll.
The government's plan to amend the interim charter also makes the picture clearer; the Borwornsak Uwanno draft charter is going to meet its fateful end; the NRC and the CDC will be dissolved; and the prime minister will appoint a new 21-member charter drafting committee to produce a more acceptable constitution.
Gen Prayut's recent comments about the NRC also point to that direction.
"It has been chaotic," he said. This is because members of the NRC are from diverse groups and from all political colours. "They are not my people. But I thought they could help the country to move forward."
"I want them to watch what I am doing and think what they should do, then design future plans for the country. But what they do must be in sync with what I am doing. Their roadmap must be clear, not just repeating 'reform, reform, reform'.
"Many politicians are now asking what needs to be reformed. How can you hope for them? They don't even know what to reform. Yet, they want an election so badly."
There is no need to interpret what the prime minister and junta leader wants. That is why many believe there is a strong possibility the Borwornsak draft charter will be dumped by the NRC, paving the way for a new political roadmap with the regime in power for at least two more years to kick start reform, draft a new charter, and produce organic laws before the poll can take place.
Be it the Borwornsak charter or a new one, the aim will remain the same - to eradicate corrupt politicians and parliamentary dictatorship.
Gen Prayut himself has repeatedly said that he risked his life to stage the coup, so he could not let it be "wasted".
All eyes are now on the Borwornsak charter drafting committee. Its amendment work will start next Tuesday and the revised draft will be sent to the NRC for deliberation on Aug 21. That is when the public will see what the amended draft charter looks like.
The NRC will have 15 days to work on the draft charter before the two-day voting session on Sept 7. Whether it is a yes or no vote, the Borwornsak drafting committee will come to an end.
With a yes vote from the NRC and the national referendum, the old political roadmap could prevail. But it looks highly doubtful this will be the case.
Nattaya Chetchotiros is Assistant News Editor, Bangkok Post.