A previous poster has provided an extract from the Malaysian AIP showing radar coverage up to 200 nm. This radar is located at Kota Bharu (WMKC), and the normal configuration of Malaysian DCA radars is a co mounted PSR (60 nm range) antenna with a MSSR antenna , range 200 nm. This is the nearest radar to the last displayed position (N6.97 E103.63) on FR24.
As this location is 93 nm from the Kota Bharu radar, it is outside PSR coverage, so no primary radar returns would have been seen. However the position is well within SSR coverage with a lowest coverage height of about 5000 ft at this range. At 200 nm the lowest coverage height is about FL270.
The SSR data from this radar is sent to the KL ATC center at Subang, which provides enroute ATS for the KL FIR.
As for other radars, the last position is about 190 nm from the Hat Yai radar site in Southern Thailand, and 290 nm from the Ho Chi Minh radar, so no other radar coverage was available.
However there is an ADS-B site on Con Son island, about 130 nm south of HCMC. This is at a elevated site of 1500 ft, so has very good coverage, and is 200 nm from the last FR24 position. The lowest coverage height is about FL220 at this range. The Con Son ADS-B data is also sent to Singapore ATC to enhance surveillance of the ATS routes in the adjacent Singapore FIR
So its likely that the various ATS providers had good position data - but entirely dependant on the aircrafts transponder/s. Without that no data at all. There could of course be military radars providing PSR coverage of this area - but that has not been disclosed as yet.