I suppose it depends what one sees as part of the plan. Reuters mentioned on Aug 27 that
Sarkozy called for international monitors to replace Russian patrols around the rebel region of South Ossetia as quickly as possible, and for talks on "security and stability modalities" there and in the region of Abkhazia to start quickly.
Each of those points matched one from his peace plan which has yet to be fully implemented, a lack of success which has raised doubts about whether the agreement is still alive.
Sarkozy, whose country holds the rotating six-month EU presidency, also stepped up his criticism of Russia's recognition on Tuesday of the two provinces.
"This decision, which aims to change Georgia's borders unilaterally, is simply unacceptable," Sarkozy said.
Clearly international peacekeepers didn't replace the Russian forces. And Russia didn't rescind recognition of those republics. Whether that was actually part of Sarkozy's "peace plan" (since it wasn't something that Medvedev signed up to) or merely discourse aimed to emphasize the difference of opinions/vision.. is anybody's guess.
Anyhow, Ilves refers to the EU starting talks with Russia on a new agreement, which also happened in 2008. However, according to Russia
The negotiations started in July 2008. Twelve negotiation rounds have taken place. At an extraordinary meeting on 6 March 2014 leaders of the EU Member States decided to suspend bilateral talks with Russia on the New Agreement «in connection with the situation in Ukraine».
So those negotiations had started a bit before the Georgia war. Another Russian page from April mentioned that
The EU and Russia agreed to hold the ninth meeting of the EU-Russia PPC [Permanent Partnership Council] on Freedom, Security and Justice in October 2008 in France.
That meeting was held as planned despite the apparent disagreements over Georgia. Whether that can be taken as Sarkozy abandoning his demands/vision (meaning those that Medvedev didn't agree to), or whether that was merely an ack that those were not realistic/realpolitik... is in eye of the beholder. I wasn't able to find any statement from Sarkozy whether he conditioned any EU (or France) cooperation with Russia on those stricter demands he made outside of the six points agreed with Medvedev.
Furthermore, an EU page mentions that there was in fact more than one document involved, even in that peace plan more narrowly construed:
The exact status of the Sarkozy-Medvedev agreement of 8 September has led to some controversy.
While the international community and the Georgian authorities insist that the 8 September agreement
outlines the first phase of the implementation of the 12 August Ceasefire agreement and in no manner
supersedes it, the Russian position seems to be that this agreement replaces certain aspects of the
Ceasefire agreement most notably with regard to the withdrawal of Russian troops. This was also clear
during the Assembly’s debate on 2 October 2008 on the consequences of the war between Georgia and Russia, when the Russian delegation sought to replace references to the Ceasefire agreement with
references to the “Sarkozy-Medvedev” agreement of 8 September 2008.
And in 2009 Russia scuppered the OSCE and UN missions in Georgia by voting against the continuation of those. The EUMM was also denied access to Russia/separatist controlled territories. However that's probably not something attributable directly to Sarkozy, unless you want to consider that he didn't seem to envision any countermeasures for those moves.