Doubt it. China never traditionally bought much weaponry from the Europe/USA so it is very hard to see what important systems a 1989 embargo would have stopped being sold.
China has had several weapon procurement phases since 1949:
Soviet-supplied. This ran all the way up to the China-USSR skirmishes in the late 60s.
(bad Russia relations): Indigenous builds (and copies). During this phase, Russia was not supplying anything so China would continue manufacturing previously acquired Russian tech and try to improve on them. A lot of their equipment was just spruced up 60s Soviet tech like say modified T-62s.
I don't know of any major Western purchases that were ongoing before the 1989 embargo. There might have been some that were stopped short, but I've never seen something like "Model T88 tank, based on German Leopard 1". So it either never happened much or it got stopped. I tend to think the first, not least because China was still dirt poor in 1989. Yes, there was some trade going on, but, no, its stoppage didn't change China's posture much, which was still relying on cloning obsolescent Soviet tech.
(For now, I am keeping both the above paragraph and the one below, because they present a more nuanced view than my original answer. If someone wants to chip in/edit, go right ahead.).
as per @o.m.'s remark, which is very much correct, French helicopters were supplied, and were manufactured locally, under license. It is very much possible that, had Tianamen not happened, broader European arms trades would have happened. One of the sources I saw while researching this talked about sizable volume of various arms trade that got cut short and France, like the UK, has in the past been very aggressive in the past about arms-trading to whoever buys. Think of it as a budding romance, cut short
- (1990 post Tiananmen) Back to business with Russia. Now richer, China went back to, now-poorer, Russia and could buy more. Its manufacturing also improved so it could clone more efficiently:
(Note: list below dates from 2005)
Since 1990, China's major arms purchases have included:
402 Russian Su-27 and Su-30 fighters (including 78 Su-27 fighters and trainers; 200 Su-27 fighters being co-produced in China; 76 Su-30MKK fighters; and 48 Su-30MK2 naval strike fighters for the PLA Navy)
12 Russian Kilo-class diesel-electric submarines
4 Russian Sovremenny-class destroyers
Russian SA-10 and SA-15 air defense missile systems.
For example, they bought a Russian aircraft carrier, mostly to develop naval air doctrine.
They've also bought weapons from Israel.
Having said all this, China is a potential future adversary and has a long history of copying foreign high tech and sometimes bettering it. Opening up arms trades with China now will only facilitate that knowledge acquisition. At best it will make China a more capable competitor in the global arms trade, eating into future Western profits. At worst, those exports may yet bite the West.
Misattributed Marx quotes about capitalists selling rope to be hung with come to mind.
Where does China buy its hi-tech weapons from other than Russia?