The reason the FAA considered fuel tank inerting in the first place is because of a 1996 crash of a 747 that killed 230 people[1], and which is thought to have been avoided had the tanks been inert[2]. Other 747s were lost to the same issue, such as the ULF48 that crashed in 1976 killing all aboard[3].
To answer your question, no, the 747 is not "safe". No aircraft ever made is "safe". They will all crash and kill people given sufficient flight hours. The question is what we consider acceptable risk, those standards change over time as technology improves, and as regulators phase out older models by sunsetting certain exceptions.
As that's done older aircraft either need to be retrofitted, or sold to jurisdictions with laxer rules.
To answer your question, no, the 747 is not "safe". No aircraft ever made is "safe". They will all crash and kill people given sufficient flight hours. The question is what we consider acceptable risk, those standards change over time as technology improves, and as regulators phase out older models by sunsetting certain exceptions.
As that's done older aircraft either need to be retrofitted, or sold to jurisdictions with laxer rules.
1. https://en.wikipedia.org/wiki/TWA_Flight_800
2. https://en.wikipedia.org/wiki/Inerting_system#Aircraft
3. https://en.wikipedia.org/wiki/Boeing_747_hull_losses#1970s