The process of renouncing Indonesian citizenship is very simple and fast, abroad and in the country. No decree is needed from the president (this is not even in the law I think, but automatism is considered) for the Ministry of Law to issue certificate that you are not a citizen as well. Indonesian citizenship is hard to get and easy to lose.It is a common knowledge that In Indonesia, dual nationality is not permitted. However, if an Indonesian acquires citizenship in another country, the process of losing Indonesian citizenship is lenghty and complicated. Only the Indonesian president can officially declare the loss of Indonesian citizenship, and this must be done through a presidential decree.
A common example, especially in the past, is children from mixed marriages who, upon turning 18, simply pretend not to hold dual nationality until they get caught. They often get caught when they request services, like asking an Indonesian passport to enable them to travel outside Indonesian territory. At that point, it is not unusual for them to be asked for an affidavit.
If I recall correctly, I have previously shared some examples of this situation in this forum. For instance, former Vice Minister Alchandra Tahar and the former regent of Sabu Raijua in East Nusa Tenggara Orient P Riwu Kore were both getting caught to hold U.S. citizenship.
Additionally, some Indonesians are born in the U.S. There are rumors that the former Indonesian president's daughter in law holds dual nationality, as she was born in the U.S., with no reports of her renouncing her American citizenship. This is similar to a former minister from former Indonesian president's cabinet. In the US Supreme Court has ruled that anyone born in the US cannot lose heir citizenship unless they voluntarily renounce it.
In Indonesia, in such cases, if getting caught they simply renounced one of their citizenships.
Another past example involves Muslim hardliners who joined ISIS and appeared in video clips provoking the Indonesian government. In response, the Indonesian president issued a decree revoking their citizenship. However, they are not considered stateless, as the Indonesian government argues they still hold citizenship with ISIS and they consider ISIS is a country at that time.
In all of the cases above noone has become stateless when their Indonesian citizenship are revoked.
If caught redhanded with two or more citizenships, in the eyes of the law you can get the consequences with or without decree, meaning you would be automatically considered foreigner, your Indonesian passport will be seized and the assets that you do not have right could be confiscated (hak milik, shares in local PTs etc).