How should mainstream science assess this discovery?
This is actually only my thought experiment, but the way I feel sure this news would be assessed by most scientists is that it definitely and triumphantly disproves that odious religious claim that life is unique to Earth and by extension, it disproves all religion as well.
Scientists, just like they are people, will do anything to hold cherished beliefs and diss fearful new ideas
(And, by the by, what religions, and where, ever claimed to know for sure Life only exists on Earth ? My religion likes to say that the ways of the Creator are mysterious and unrevealed in the main.)
Still, almost with one voice, the science community would sing out "Life on Mars exists, more examples will eventually be found eventually (keep those cards and grants coming in !) and Life will soon be found on other planets - potentially hundreds of millions of them throughout the Universe - some with lifeforms as multi-celled and complex as us.
All based on seven little blobs.
Whenever people - and I include scientists in that group - really really want to believe something, they will twist the few facts this way and that in their favour.
But if they really really want to dis believe something, they are just as skilled to find ways to twist the few facts against itself.
By way of example :
HGT and Endosymbiosis , two - now well established - major additions to the dog eat dog republican-conservative-free-enterprise-cum-Darwin version of Evolution were both proposed as major biological phenomena by a few scientists way back in the 1920s, albeit based on only a few well established examples.
Think of the evidence for these theories as being much better established in the 1920s than are those seven lonely bacteria cells on Mars at the top of my thought-experiment, but no where as widely established as these theories are today.
Science's 'rare exception' Big Lie
So back in the 1920s, they were not - nor could not - be dismissed as having never happened, but they were instead 'explained away' as being but 'rare' exceptions to Darwin's universal theory and so they were justified in being ignored as a consequence.
But even one sustained exception is a billion too many when it comes to any theory - it means the theory must be re-tooled ---- as those seven lonely living bacteria from Mars would do to any theory holding Life to be exclusive to this "Rare Earth".
(Let me be clear - those seven tiny blobs from Mars would force me to strongly consider Life all through the Universe as distinctly likely.)
But the real objection to these twin theories back then was that Twenties elite scientists and Twenties elite society could not abide the thought that Man (them) had not come about strictly by His own efforts, mutating His way ever upwards out of the primeval slime.
The thought that instead the supposedly primitive slime had freely offered up human complexity by horizontally inserting their genes into larger beings was unbearable to think about.
It would be like proving that some darkie slave boy had actually taught Newton the entire Theory of Gravity !
Public is not Popular - that is where Science censors
Again, may I add before hostile scientists do it for me, that these new theories were published in well regarded journals back in the 1920s.
They were not informally censored (but plenty of scientists were and still are by their lab chiefs), but only because their authors stuck to their guns, ignored their senior colleagues and shopped around for a journal editor willing to take them in.
But making something public is never the same as making it popular and thus part of mainstream science and taught to students.
This is the real power of senior elite scientists (yesteryears' rebels), to be able to prevent new ideas taking this further step --- at least until the seniors guys are all dead.
In my view, 99% of middle-aged scientists never ever change their minds about their core beliefs from their early adult years and that as a result, science only advances as fast as each new golden watch and funeral.
Post 1945 science reassesses the old in light of Penicillin & Auschwitz twin shocks
As I have said many times and will keep on doing so, post-Auschwitz & Penicillin science often did not really discover much that wasn't already known by 1940.
They just re-assessed its importance through new eyes.
Sometimes - often - we mean by this literally as the physically new eyes of those so young that they have no institutional history to defend.
But in this specific case, I mean that new Baby Boomer scientists metaphorically saw the world with new ideological and intellectual eyes, after growing up on the consequences of the top and bottom assaults on Modernity by Auschwitz and Penicillin...