*shrug*
reallistically?
They will likely have support in Parliament against article155 from Podemos (leftist party, 69 seats), the Basque Nationalist party (5 seats), EH Bildu (another Basque nationalist party, 2 seats). This is plus their own 17 seats combining CDC and ERC. Soo... at most 93 votes. Out of a total of 350. So certainly not enough to turn this around with voting against the Unholy Trinity of PP, PSOE, and Cs (really Cs has like 32 seats, so basically they're acting as mamporreros in this union. Doesnt keep them from pretending they're important)
Or you meant international support? Noone that will lift a finger. I mean, Donald Tusk and some other people certainly said that there should be a negotiation, but I don't really expect them to lift a finger. You know how these things work.
Both domestic and international really, though sucks that Catalonia doesn't have much support at the federal level - even for negotiations? That said, despite Catalonia's small size they are pretty wealthy, and for all the EU's talk of diplomatically isolating a nascent Catalonia their hunger for european clay would be unlikely to leave a gap in the Mediterranean sea - so for cynical purposes they would seek to expand into an independent Catalonia. Imo an independent Catalonia should stay outta EU but that's up to Catalonians really to decide. Of note is the divide between Macedonia and Greece, with Macedonia being blocked by Greece
over names. So Spain could feasibly frustrate Catalonia's diplomatic efforts after a potential declaration of independence.
That said, if Catalonia put 2% of their GDP into defence they'd have $5.1B to arm themselves with, which would allow them to field a defence force somewhere in between Singapore and Qatar. With no naval base of their own and near all training facilities based in Spain outside of Catalonia, again Catalonia would be a bit stuffed there.
But it wouldn't be impossible to turn all that around. Right now Catalonia probably shouldn't pursue independence simply because Spain has her quite literally surrounded, but surely a 15 year long plan would give Catalonia the strength needed to choose Madrid or Barcelona? At the very least, the strength needed to have a Madrid government hear their words. Overconfidence can kill, patience too, but the latter less likely to.
Also of note is I've been looking at the response from UK, France, Italy, USA & Russia, and it is looking absolutely not good for the most part. I reckon despite the governments' lack of any formal statements, much of the UK is sympathetic because of the way the Spanish government has treated Gibraltarians with the Guardia Civil, but the state itself is neutral.
France opposes unilateral independence, but what measures they would take in such an event where the Spanish military marched upon Catalonia is anyone's guess. Doubt it would be the same as Belgium though...
Italy is opposed in all cases, concerned as they are with Lombard or Venetian separatist movements, and
Russia appears to be supporting both sides. Which is very Russian. USA also in favour of Madrid, though not terribly committed.
On the bright side, most of those nations also oppose Madrid using excessive force. Could Catalonia endure, and most importantly, renegotiate its position and regain autonomy if subjected to direct rule of law within a politically divided society?